When performing a staged update to compressed images,
ensure that the bufferRowLength and bufferImageHeight
is a multiple of the compressed texel block

Bug: angleproject:5017
Test: angle_end2end_test --gtest_filter=*ETC1CompressedImageNPOT*
Change-Id: I54327ec610d1050465d112c7eff385d19dc0c390
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2393754Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>