Capture/Replay: Don't capture XFB 0 in MEC. This will only add an extra unused XFB object. Noticed when capturing from the T-Rex replay. Bug: angleproject:5134 Change-Id: Ia368f9e9f59f9ea7473ac88928a413001fa99496 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2449157 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com>