getFramebufferAttachmentParameter returns incorrect
result for framebuffers in an inconsistent state.

BUG=angleproject:2281

Change-Id: Ifb83ecaf16c95bf1237b2c4f2684de6aa2d55c46
Reviewed-on: https://chromium-review.googlesource.com/823224
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>