Curve Data: Answer checking is currently slow

[robx]

Curve Data: Answer checking is currently slow, and sometimes freezes completely. For example, here (source), instead of the "obvious" solution, spiralling inwards from the top left anticlockwise currently freezes the tab on my computer.

Originally posted by @edderiofer in https://github.com/robx/pzprjs/issues/1#issuecomment-525831908

[robx]

@x-sheep another one! I've added this as test-cases in https://github.com/robx/pzprjs/commit/564df77ef6fd5812fb9cc5a3d5fd2684287f7f5b (but the problematic one is commented; I didn't wait for it to finish)