fix a crash in box2d (that also crashes kolf)

with some data extracted from a kolf course, box2d calculates a
negative area, that is not possible in Real*Real vector space.

fixed using the abs area of each triangle.

Also filled a bug in box2d (I have had to use okteta to bypass their
captcha).

BUG: 258998
FIXED-IN: 4.10
REVIEW: 107739