Fixed more bugs.

* Fixed a bug where UBFG crashes occasionally because the QPainter doesn't get 'released' and the texture its painting to gets changed.
* Fixed a bug where right and/or lower border on glyphs for non-alpha images caused black lines to show along those edges.
* Fixed a bug where index8 non-transparent images were not being exported properly (as a result of commit cb3cdde81133347a9d0cb0ee13f3cc5717168593)
* Fixed a bug where index8 non-transparent backgrounds were getting dithered.