When projection painting a dense mesh a face can be marked
PROJ_FACE_DEGENERATE when it is too small. Degenerative faces are
handled differently and as documented can create incorrect results.
Not sure what these incorrect results are and if there could be a better
solution for handling these results.
This fix would only mark a face degenerative when all the verts are the
same.
Reviewed By: Campbell Barton
Differential Revision: https://developer.blender.org/D7662
c9360b239b