Metal: Protect against invalid locations in setUniformImpl Chrome disables validation and a common bug is that the wrong program is used during uniform setting in Skia. Make this bug less catastrophic while the root cause is investigated. Bug: chromium:1484878 Change-Id: I521e99cdf6cebc56775e484fa8d61ad18f506479 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4886384 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>