Metal: ANGLE Metal AutoObjCPtr == nullptr comparison is inverted Port the fix from Webkit for this inverted comparsion Unify the nullptr type throughout all functions Bug: angleproject:6351 Change-Id: Id856af31c9eea5cc79993c3454e452d1c14d0d0e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3169436 Commit-Queue: Kenneth Russell <kbr@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Le Hoang Quyen <le.hoang.q@gmail.com> Reviewed-by: Gregg Tavares <gman@chromium.org>