Porting bug

[adnanutayim]

Hello there,

Thanks for implementing S2 in golang!

We found what seemed to be a small porting issue in Loop.go
We noticed that Loop.Contains(o *Loop) returns false sometimes when o is properly contained. We traced this issue to hasCrossingRelation().
This function doesn't share the same logical control flow with the original c++ version.

In the go version, currently it returns false when the crossing target for A is satisfied. We believe it should return false when the crossing target is not satisfied.
So this line might need a not operator at the beginning so it looks like this:

 if !containsCenterMatches(aClipped, l.aCrossingTarget) {...}