eevee_geom_world_vert.glsl and eevee_geom_volume_vert.glsl do not
support shadows, but the shader validation pipeline still compiles the
shadow variant of these shaders. This results in the fragment shader
reading from inputs that are not written to as vertex shader outputs.
On the Intel Windows OpenGL driver, this leads to a shader linking
failure. This PR avoids the issue by writing zeros to the interface
variables when MAT_SHADOW is defined.
16ad7524a7