Crash when quitting after attempting to cancel a data composition addition

Steps

On both 0.6.2 and the latest sources:

1. Create data composition
2. Select a directory with many files, such as a directory for a project that uses NPM
3. Click cancel (not exit) on the addition dialog (note that cancel doesn't visually do anything right now)
4. Exit Xfburn
5. See "Segmentation fault" in the terminal

Traceback

[New LWP 1049584]
[New LWP 1049585]
[New LWP 1049587]
[New LWP 1049586]
[New LWP 1049635]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `./xfburn/xfburn'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007ffb966b06e9 in g_type_check_instance_is_fundamentally_a () from /lib/x86_64-linux-gnu/libgobject-2.0.so.0
[Current thread is 1 (Thread 0x7ffb94f8af40 (LWP 1049584))]

Thread 5 (Thread 0x7ffb6ebfd640 (LWP 1049635)):
#0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1  0x00007ffb965e170c in g_cond_wait_until () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007ffb965623e1 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3  0x00007ffb96562566 in g_async_queue_timeout_pop () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#4  0x00007ffb965c4749 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#5  0x00007ffb965c1a41 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#6  0x00007ffb96294b43 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#7  0x00007ffb96326a00 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

Thread 4 (Thread 0x7ffb9336a640 (LWP 1049586)):
#0  0x00007ffb96318d7f in __GI___poll (fds=0x55dc7a55eb70, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007ffb965e7696 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007ffb965903c3 in g_main_context_iteration () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3  0x00007ffb941a733d in  () at /usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so
#4  0x00007ffb965c1a41 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#5  0x00007ffb96294b43 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#6  0x00007ffb96326a00 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

Thread 3 (Thread 0x7ffb92b69640 (LWP 1049587)):
#0  0x00007ffb96318d7f in __GI___poll (fds=0x55dc7ae75760, nfds=6, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007ffb965e7696 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007ffb96592293 in g_main_loop_run () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3  0x00007ffb9693cc1a in  () at /lib/x86_64-linux-gnu/libgio-2.0.so.0
#4  0x00007ffb965c1a41 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#5  0x00007ffb96294b43 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#6  0x00007ffb96326a00 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

Thread 2 (Thread 0x7ffb93b6b640 (LWP 1049585)):
#0  0x00007ffb96318d7f in __GI___poll (fds=0x55dc7a55a3f0, nfds=2, timeout=6474) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007ffb965e7696 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007ffb965903c3 in g_main_context_iteration () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3  0x00007ffb96590411 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#4  0x00007ffb965c1a41 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#5  0x00007ffb96294b43 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#6  0x00007ffb96326a00 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

Thread 1 (Thread 0x7ffb94f8af40 (LWP 1049584)):
#0  0x00007ffb966b06e9 in g_type_check_instance_is_fundamentally_a () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#1  0x00007ffb96699c1f in g_object_unref () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#2  0x00007ffb96da78e9 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#3  0x00007ffb9668bc6c in g_closure_invoke () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#4  0x00007ffb966a7ae0 in  () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#5  0x00007ffb966a9554 in g_signal_emit_valist () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#6  0x00007ffb966a97a3 in g_signal_emit () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#7  0x00007ffb96da7600 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#8  0x00007ffb96699e71 in g_object_run_dispose () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#9  0x00007ffb96b2c6f0 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#10 0x00007ffb96b7702a in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#11 0x00007ffb9668bc6c in g_closure_invoke () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#12 0x00007ffb966a7ae0 in  () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#13 0x00007ffb966a9554 in g_signal_emit_valist () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#14 0x00007ffb966a97a3 in g_signal_emit () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#15 0x00007ffb96da7600 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#16 0x00007ffb96699e71 in g_object_run_dispose () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#17 0x00007ffb96db8689 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#18 0x00007ffb96b7702a in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#19 0x00007ffb9668bd2f in g_closure_invoke () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#20 0x00007ffb966a7ae0 in  () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#21 0x00007ffb966a9554 in g_signal_emit_valist () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#22 0x00007ffb966a97a3 in g_signal_emit () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#23 0x00007ffb96da7600 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#24 0x00007ffb96db70ee in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#25 0x00007ffb96699e71 in g_object_run_dispose () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#26 0x00007ffb9668bd2f in g_closure_invoke () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#27 0x00007ffb966a7b76 in  () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#28 0x00007ffb966a9554 in g_signal_emit_valist () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#29 0x00007ffb966a97a3 in g_signal_emit () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#30 0x00007ffb96da7600 in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#31 0x00007ffb96db70ee in  () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#32 0x00007ffb96699e71 in g_object_run_dispose () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#33 0x00007ffb96c52671 in gtk_main_do_event () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#34 0x00007ffb97338743 in  () at /lib/x86_64-linux-gnu/libgdk-3.so.0
#35 0x00007ffb9736ff56 in  () at /lib/x86_64-linux-gnu/libgdk-3.so.0
#36 0x00007ffb96592d1b in g_main_context_dispatch () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#37 0x00007ffb965e76f8 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#38 0x00007ffb96592293 in g_main_loop_run () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#39 0x00007ffb96c48cfd in gtk_main () at /lib/x86_64-linux-gnu/libgtk-3.so.0
#40 0x000055dc784b63d6 in main (argc=<optimized out>, argv=<optimized out>) at xfburn-main.c:403