__gfx__ and __gff__ sections filled out unnecessarily
Seems like when to_lines is called for __gfx__ and __gff__ we end up with a bunch of empty data rows we don't need if those sections aren't full already. Not really the end of the world, but inflates the file size more than necessary.

I took a look at the code but wasn't able to quickly figure out why these sections behave differently than others.