Passing COLOR_ATTACHMENTm, where m is greater or equal to
MAX_COLOR_ATTACHMENTS, to a FramebufferTexture* function should
generate an INVALID_OPERATION instead of an INVALID_VALUE error.

BUG=angleproject:2106
TEST=angle_end2end_tests

Change-Id: I99045defcbe5eb2afefac1b45062ee4245f50dd3
Reviewed-on: https://chromium-review.googlesource.com/569966Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>