Frame Capture: Allow for no FBO when running MEC. Multi-context captures use the surfaceless context extension. That was crashing MEC because we were assuming the context would have a Framebuffer. Bug: angleproject:5133 Change-Id: I6be12d332f4754f80c088d88973219327eca251a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3352084 Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>