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>