This could lead to blitting depthStencil buffer incorrectly.

Bug: angleproject:6140
Change-Id: I2c5786c0375f8e2fefe862da68929340844ce9ae
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3009736Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>