Fix non-square scalar-to-matrix constructors. This fixes some broken tests in dEQP: functional.shaders.conversions.scalar_to_matrix BUG=angle:712 Change-Id: Ia01d720307ea6ca70da266b2085a878eaaab2412 Reviewed-on: https://chromium-review.googlesource.com/210881 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Nicolas Capens <capn@chromium.org>