Metal: Refactor hasValidRenderTarget checks Separate the computation of hasValidRenderTarget into a function and only call it if the cheaper check to allowRenderpassWithoutAttachment returns false. Bug: chromium:1329376 Change-Id: Id20a33913b7133a5aea82f53abb0a86664b4f2c6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4615188 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>