The lower bound for chroma components is size.y + 1/2, not
size.y - 1/2.

dxgi: Return DXGI_ERROR_INVALID_CALL when given a NULL mode_count in dxgi_output_GetDisplayModeList().

At some point DXGID3D10CreateDevice() started always returning
E_NOTIMPL. My guess would be that that was with the introduction of
d3d11.

In particular, actually test the return codes for most calls.