Account for zero vector axes in Mat4::Rotate(...) When the axis passed in to the Rotate function is (0, 0, 0), normalizing that vector will result in NaN values. Prevent this by returning an identity matrix and early out instead. Bug: angleproject:2306 Tests: MatrixBuiltinsTest.RotateAxisZero Change-Id: I65fd0b9944885daf56a4a35201d424e7f0aa9ba6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5333834 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>