offset_meet creates offset lines that can't be directly intersected, so
the average of the points on each offset line is 'dropped' onto the
faces around the beveled vertex, which can depend on where
the loop starts.
This fix skips faces with the same normals as the "in plane" faces from
build_boundary.
Reviewed By: howardt
Differential Revision: https://developer.blender.org/D6521
c56526d8b6