fix incorrect TexImage3D params w/ UNPACK_IMAGE_HEIGHT

Bug: 804123
Test: http://github.com/KhronosGroup/WebGL/pull/2646
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ifbce9b93f0b35817881e1e34930cbac22a1e8b98
Reviewed-on: https://chromium-review.googlesource.com/1053573
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558962}