HD SGA font doesn't work anymore

Tried to apply my double resolution SGA font (ascii_sga.png) to the game, the game doesn't display anything when using white font on a transparent png and only displays empty boxes when using the same png palette than the vanilla textures. Note that the unicode font now uses ttf files instead of a texture and  therefore is vector-based, not making this a problem for it anymore. For remaining issues with ascii.png, see MC-132708.