Add extra validation of null pointers for certain APIs Bug: angleproject:409110245 Change-Id: I25dfdbdc52cdb0d7d2a91d773a0f3600e370f139 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6440146 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Alexey Knyazev <lexa.knyazev@gmail.com> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>