Fixed crash due to NULL pointer return from SFRecoverFile().

SFRecoverFile() returns NULL if recovery was unsucessful or the user
declines it.  In those cases, the user should not be prompted to save
the font, the lack of existence of which causes a NULL pointer
dereference in the call to gwwv_ask().
Merge pull request #445 from blipvert/fixes/12

Fixed crash due to NULL pointer return from SFRecoverFile().