Fix string leak in thunar_io_jobs_load_statusbar_text_for_folder

Leak report

Direct leak of 18 byte(s) in 1 object(s) allocated from:
    #0 0x644d3be0a859 in malloc (/usr/asan/bin/thunar+0x498859)
    #1 0x7be0fddd5062 in g_malloc glib/gmem.c:100:13
    #2 0x7be0fde118d2 in g_strdup glib/gstrfuncs.c:323:17
    #3 0x7be0fdfd3eee in g_strdup_inline glib/gstrfuncs.h:321:10
    #4 0x7be0fdfd3eee in value_lcopy_string gobject/gvaluetypes.c:316:17
    #5 0x7be0fdf8a19d in g_object_get_valist gobject/gobject.c:3271:7
    #6 0x7be0fdf8aa1b in g_object_get gobject/gobject.c:3366:3
    #7 0x644d3c006919 in thunar_io_jobs_load_statusbar_text_for_folder thunar/thunar-io-jobs.c:1996:3
    #8 0x644d3c14b967 in thunar_standard_view_update_statusbar_text_idle thunar/thunar-standard-view.c:2381:44
[...snip...]

Steps to reproduce

• #1441 (comment 94585)

Testing

• No issues were detected with LSan, ASan, or Valgrind when testing the patch