Fix feedback loop clearing detection. Bug: angleproject:4517 Change-Id: I3231b129718019f83495843404cd011eb2cd480d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2122689 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tobin Ehlis <tobine@google.com>