Description of problem:
1)  Create an empty directory; e.g.
$ mkdir -- '/tmp/gthumb-bug'

2)  Copy two identical image files into that directory; e.g.
$ for i in 1 2 ; do cp -- /usr/share/pixmaps/fedora-logo.png "/tmp/gthumb-bug/fedora-logo-${i}.png" ; done

3)  Open gThumb and enable the "Find Duplicates" extension under "Preferences", "Extensions".   Restart gThumb if prompted.

4)  Invoke the "Find Duplicates" function with the following parameter values:
Start at:  /tmp/gthumb-bug
Include sub-folders:  enabled
Filter:  Media

5)  Press the "Find" button.  A new dialog should appear reporting 1 duplicate.

6)  Press the "Select" button, and select the "leave the oldest duplicates" menu item.

7)  Press the "Delete" button.  gThumb should quit unexpectedly.

Version-Release number of selected component:
gthumb-3.4.0-2.fc22

Additional info:
reporter:       libreport-2.6.2
backtrace_rating: 4
cmdline:        gthumb .
crash_function: gth_browser_exec_task
executable:     /usr/bin/gthumb
global_pid:     3977
kernel:         4.1.8-200.fc22.x86_64
runlevel:       N 5
type:           CCpp
uid:            1000

Truncated backtrace:
Thread no. 1 (10 frames)
 #0 gth_browser_exec_task at gth-browser.c:5519
 #1 delete_file_permanently at gth-file-source-vfs.c:664
 #2 delete_permanently_response_cb at gth-file-source-vfs.c:679
 #7 _g_closure_invoke_va at gclosure.c:831
 #10 gtk_button_do_release at gtkbutton.c:1899
 #11 gtk_real_button_released at gtkbutton.c:2017
 #16 multipress_released_cb at gtkbutton.c:613
 #17 ffi_call_unix64 at ../src/x86/unix64.S:76
 #18 ffi_call at ../src/x86/ffi64.c:525
 #19 g_cclosure_marshal_generic_va at gclosure.c:1561