Don't query GL_ACTIVE_SUBROUTINE_UNIFORM_LOCATIONS if no subroutines
Don't query GL_ACTIVE_SUBROUTINE_UNIFORM_LOCATIONS if no subroutines

* Works around some mesa debug message spam if no subroutines exist.

cgmb/renderdoc,googlestadia/renderdoc,baldurk/renderdoc,cgmb/renderdoc,michaelrgb/renderdoc,baldurk/renderdoc,TurtleRockStudios/renderdoc_public,baldurk/renderdoc,michaelrgb/renderdoc,etnlGD/renderdoc,TurtleRockStudios/renderdoc_public,googlestadia/renderdoc,michaelrgb/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,googlestadia/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,michaelrgb/renderdoc,TurtleRockStudios/renderdoc_public,googlestadia/renderdoc,etnlGD/renderdoc,TurtleRockStudios/renderdoc_public,etnlGD/renderdoc,Zorro666/renderdoc,cgmb/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,cgmb/renderdoc,TurtleRockStudios/renderdoc_public,etnlGD/renderdoc,googlestadia/renderdoc,cgmb/renderdoc,baldurk/renderdoc,etnlGD/renderdoc,michaelrgb/renderdoc,googlestadia/renderdoc,etnlGD/renderdoc,TurtleRockStudios/renderdoc_public,baldurk/renderdoc