#23 Crash during image move

[Scot Wilcoxon]

Using drag-and-drop in Thumbnail window from tabbed
thumbnail pane to directory pane sometimes works.
Within a few moves (either single or multiple files)
GImageView segfaults. RH 9, 0.2.25.

This makes it quite awkward to use the program to
sort/arrange images. Running the program again usually
shows the file move completed, but sometimes a file is
left behind -- or less often the file was moved but the
thumbnail remains visible until another restart.