D3D11: Re-check disabled attribs on VAO switch. When switching VAOs, if we switch to a VAO which has disabled attributes, we could occasionally in some edge cases not have a buffer initialized to render with. Fix this by re-checking the current value (disabled) attributes every VAO switch. Probably a regression caused by d28758d: "D3D11: Re-enable updateVertexBuffer dirty bits." BUG=angleproject:2156 BUG=angleproject:1156 Change-Id: Ic1795f914b9b4fa846241b0b4f9a8fe9c1183320 Reviewed-on: https://chromium-review.googlesource.com/669963 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>