winex11: Failing to create a context in X11DRV_wglCreateContextAttribsARB() is not an internal error.

In particular, without WGL_WINE_query_renderer, the only way to determine
whether a particular context version is supported or not is by attempting to
create a context with that version.
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>