Incorrect hull for points on a square pattern

[andreesteve]

Points distributed in a square pattern now have an incorrect hull (left side is v1 delaunator-rs, and right side is the latest delaunator js):

Here's the result for v0.2.1 that shows the hull matched the js result

Likely a regression from the robust checks.

[andreesteve]

Here's the smallest repro I found far.