WebGLCompat: Fix depthstencil query results. getFramebufferAttachmentParameter returns incorrect result for framebuffers in an inconsistent state. BUG=angleproject:2259 Change-Id: I76fa99f1b8847c30469d344bd93dedd9cf6657bf Reviewed-on: https://chromium-review.googlesource.com/798318 Reviewed-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>