Fix T66348 Eevee: Broken shader if using textures and shader_to_rgb node

Was caused by a missing texture resource.

source/blender/nodes/shader/nodes/node_shader_shaderToRgb.c

@@ -38,6 +38,10 @@ static int node_shader_gpu_shadertorgb(GPUMaterial *mat,
                                        GPUNodeStack *in,
                                        GPUNodeStack *out)
 {
+  /* Because node_shader_to_rgba is using fallback_cubemap()
+   * we need to tag material as glossy. */
+  GPU_material_flag_set(mat, GPU_MATFLAG_GLOSSY);
+
   return GPU_stack_link(mat, node, "node_shader_to_rgba", in, out);
 }