getFramebufferAttachmentParameter returns incorrect
result for framebuffers in an inconsistent state.

BUG=angleproject:2259

Change-Id: I76fa99f1b8847c30469d344bd93dedd9cf6657bf
Reviewed-on: https://chromium-review.googlesource.com/798318Reviewed-by: Bryan Bernhart <bryan.bernhart@intel.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>