fontBuilder: add glyphDataFormat=0; error with accidentally cubic outlines

[anthrotype]

Fixes #3113

[justvanrossum]

LGTM, although I don't quite understand the use for the checkFormat argument.

[anthrotype]

I don't quite understand the use for the checkFormat argument.

Initially I didn't have that, but then I thought that checking all glyf glyph flags may be relatively expensive operation to be doing all the time and if a client knows that all the glyphs that are passed to the fontBuilder have already been cu2qu'ed beforehand.. it's just a waste of time.

[justvanrossum]

Initially I didn't have that, but then I thought that checking all glyf glyph flags may be relatively expensive operation to be doing all the time and if a client knows that all the glyphs that are passed to the fontBuilder have already been cu2qu'ed beforehand.. it's just a waste of time.

Ahh, that makes a lot of sense. Maybe reword the doc string to make it clearer that that is what it's for? And/or consider calling it validateGlyphFormat? (Or anything else with the word validate in it.)

[anthrotype]

ok, will do Done