FOLD import robustness

[edemaine]

Generating FOLD files in some code of mine, I noticed the following import robustness issues:

• If the FOLD has edges (edges_vertices and edges_assignment, and maybe certain subsets thereof, maybe even in all cases?), then it's required to also have edges_foldAngle. Should default to 180 for valleys, -180 for mountains, and 0 for others.
• If edges_assignment has an unsupported value, then the program crashes. It should instead report an error dialog, like when there are unsupported colors in an SVG file, and default to something (U I guess?).

[hendursaga]

Not sure if this goes here, but one of the examples in the official FOLD spec does not fold properly, at least, initially.

When I first import it, it looks something like this:

But when I import it a second or third time, it usually looks like this:

I'm not sure what is going on. Even in the latter case, when it does fold, any change in the fold percentage and it's all haywire again.