Don't show modal error when opening a folder as a font fails
Win32: Another case of backslashes to slashes.

This fixes most of the *crashes* in #1803, but not necessarily
what may be considered as 'logic' bugs.
Alter the file open method to work more sanely.

* If a file open action fails (could not load path as a font), then a best-effort
  attempt is made to return the user to the last directory they were at, otherwise
  they will be returned to the default folder.
* If a folder is 'opened' but is not actually a font, then the file opener will
  be redisplayed starting at the contents of that folder.