Font view leaks on hilite moves w arrow keys

fontforgeexe/fontview.c routine SCPreparePopup() leaks strings on each call.
This can be provoked as simply as scanning through glyph cells using arrow
keys.  Not a big leak, less than 20 bytes per call.

Fix saves and free()s the intermediate results strings.
Merge pull request #1611 from tshinnic/leak_fontview_char_description

Font view leaks on hilite moves w arrow keys