[checkoutlinesufo] restore_contour_order fails in some situations

[punchcutter]

In some outlines like the glyph in tests/checkoutlinesufo_data/input/contour-restore.ufo checkoutlinesufo fails to restore contour order because of the way the contours overlap by a single point.

Run
checkoutlinesufo -e --all contour-restore.ufo

and the result is

AssertionError: Failed assertion: duplicated start point on contour 3 at 616, 597 of glyph cid51107.

This stops the entire process, but we should never fail here. The main purpose of restore_contour_order is to attempt to keep compatibility the same across masters, but that's not always going to be possible, especially when removing overlaps. If we can't restore contour order then we should just report it.

[frankrolf]

Related to #790, perhaps?

[punchcutter]

Maybe related, but all of the files attached to #790 seem to work fine with the current checkoutlinesufo