GL: Fix possible shift by -1

This can happen when the attribute has been optimized out by the compiler.

source/blender/gpu/opengl/gl_vertex_array.cc

@@ -70,7 +70,7 @@ static uint16_t vbo_bind(const ShaderInterface *interface,
       const char *name = GPU_vertformat_attr_name_get(format, a, n_idx);
       const ShaderInput *input = interface->attr_get(name);
 
-      if (input == nullptr) {
+      if (input == nullptr || input->location == -1) {
         continue;
       }