Fix leak in _thunar_search_folder

Leak report

Direct leak of 24 byte(s) in 1 object(s) allocated from:
    #0 0x5f07285d97b9 in malloc (/usr/local/bin/thunar+0x4987b9)
    #1 0x76dcaacdce4a in g_malloc /usr/src/debug/glib2/build/../glib/glib/gmem.c:100:13
    #2 0x76dcaacd198b in g_list_prepend /usr/src/debug/glib2/build/../glib/glib/glist.c:253:14
    #3 0x5f07287d8927 in _thunar_search_folder thunar/thunar-io-jobs.c:1603:23
    #4 0x5f07287d88bd in _thunar_search_folder thunar/thunar-io-jobs.c:1593:11
    #5 0x5f07287d88bd in _thunar_search_folder thunar/thunar-io-jobs.c:1593:11
    #6 0x5f07287d2f01 in _thunar_job_search_directory thunar/thunar-io-jobs.c:1658:3
    #7 0x5f072891061f in thunar_simple_job_execute thunar/thunar-simple-job.c:119:13
    #8 0x76dcabec28cf in exo_job_scheduler_job_func /home/s/code/exo/exo/exo-job.c:310:13
    #9 0x76dcaae3e619 in io_job_thread /usr/src/debug/glib2/build/../glib/gio/gioscheduler.c:75:16
    #10 0x76dcaae738d5 in g_task_thread_pool_thread /usr/src/debug/glib2/build/../glib/gio/gtask.c:1583:3
    #11 0x76dcaad0d372 in g_thread_pool_thread_proxy /usr/src/debug/glib2/build/../glib/glib/gthreadpool.c:336:15
    #12 0x76dcaad071b5 in g_thread_proxy /usr/src/debug/glib2/build/../glib/glib/gthread.c:835:20
    #13 0x5f0728515c6d in asan_thread_start(void*) (/usr/local/bin/thunar+0x3d4c6d) (BuildId: 4393f5858fee53d0)
    #14 0x76dcaaabe39c in start_thread /usr/src/debug/glibc/glibc/nptl/pthread_create.c:447:8
    #15 0x76dcaab4349b in __GI___clone3 /usr/src/debug/glibc/glibc/misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78

Testing

• I didn't see any new LSan or ASan errors after applying the patch and testing searches