The OpenGL ES 3.0.5 spec section 3.8.10.5 states: "For cube map
textures an INVALID_OPERATION error is generated if the texture
bound to target is not cube complete".

Change-Id: I4304ecf125528b9406a011a95d7822b1f868ee14
Reviewed-on: https://swiftshader-review.googlesource.com/15328Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>