This prevents newer group keys from overwriting old ones.
Prevents bugs from creeping in like happened during texture buffer
development.

Bug: angleproject:3573
Change-Id: Iea69cac988e2cf4802a9f64c54cb694d32f1d3e1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2521238Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>