Reset cache in ProgramExecutable::updateActiveSamplers. This missing reset was causing incorrect state validation to persist in a few instances. Bug: chromium:1266437 Change-Id: I7ab47c81bf9f855e3ad75048f9d1aaefbc2291df Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3262477 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>