D3D11 Feature Level 9_3 can't disable mipmaps on a mipmapped
texture, and sample from level zero of it. A previous commit
added a workaround for this in ANGLE to Texture2Ds. This
commit fixes some minor issues in that commit, and extends
the workaround to apply to TextureCubes too.

Change-Id: Ic97321af6f8bbf7ad5d96e58655c342db3978a6a
Reviewed-on: https://chromium-review.googlesource.com/241944Tested-by: Austin Kinross <aukinros@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>