shader: Make sure to use textureSize with the correct arguments

In the case of gsampler2DRect, there is no second argument to be provided to
textureSize.

Makes the `spec@arb_texture_rectangle@copyteximage rect samples=2` not crash.

Signed-off-by: Corentin Noël <corentin.noel@collabora.com>
Part-of: <https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/761>
1 file changed