This will avoid breaking render pass if clearing depth in clearWithDraw.

Bug: angleproject:4836
Change-Id: I50242d1115efc91059923143f6ae5fd25fb3d36f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2462717
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Charlie Lao <cclao@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>