pinned width/height constraint getters return internal constraints

[ZevEisenberg]

Using the methods in RZUtils to retrieve the pinned width or height constraints of a view may sometimes return instances of NSContentSizeLayoutConstraint when you would expect them to return nil. This seems to be an internal representation of the intrinsic content size. Discovered by @jvisenti and @KingOfBrian.

[ZevEisenberg]

This should be prevented against (make sure constraint is not a subclass of NSLayoutConstraint?) or at least well-documented, but I personally prefer just not to use these methods, and to keep track of the constraints myself.