Fix regression with GetNextGLSLAttributeType. A refactoring bug slipped in that used the non-transposed row count for non-square matrices, causing an ASSERT failure in Debug. It's unfortunately not easy to revert the previous change, so instead fix it here. BUG=angleproject:1129 Change-Id: I0de66de46a24b402c93da68f189a2c65616c2006 Reviewed-on: https://chromium-review.googlesource.com/294641 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>