When updating ImageHelper::flushStagedUpdates to handle base and
max texture level, we got off by one when deciding if an update
landed in in the range of the current vkImage. When there are 8
mipLevels and we see an update for level 8, that should not be
applied, and should be preserved in updatesToKeep.

Bug: angleproject:3950
Test: MipmapTest.DefineValidExtraLevelAndUseItLater/ES2_Vulkan
Change-Id: I63e0c24f7885f8b0580ce212b531711aebcf0e01
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1848933Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Cody Northrop <cnorthrop@google.com>