arb_shadow: fallback to a not shadow sampler for a not depth texture
It is undefined behavior when an ARB assembly or shadow2d GLSL func uses SHADOW2D target with a texture in not depth format.
In this case AMD and NVIDIA automatically replaces SHADOW sampler with a normal sampler and some games like Penumbra Overture which abuses this UB works fine but breaks with mesa.
Signed-off-by: Illia Polishchuk illia.a.polishchuk@globallogic.com