brightness-contrast-effect: Don't actually run if it will have no effect
brightness-contrast-effect: Don't actually run if it will have no effect

Don't run the shader and redirect to an FBO if it won't actually do anything.
This saves us on resources a ton.

https://bugzilla.gnome.org/show_bug.cgi?id=683066

heysion/clutter-clone,djdeath/clutter,heysion/clutter-clone,djdeath/clutter-android,djdeath/clutter,Distrotech/clutter,Distrotech/clutter,GNOME/clutter,GNOME/clutter,heysion/clutter-clone,jigpu/clutter,jigpu/clutter,djdeath/clutter-android,ebassi/clutter,Distrotech/clutter,ebassi/clutter,jigpu/clutter,GNOME/clutter,djdeath/clutter-android,djdeath/clutter-android,jigpu/clutter,collects/clutter,ebassi/clutter,jigpu/clutter,ebassi/clutter,Distrotech/clutter,djdeath/clutter,djdeath/clutter,collects/clutter,jigpu/clutter,collects/clutter,djdeath/clutter,djdeath/clutter-android,Distrotech/clutter,heysion/clutter-clone,heysion/clutter-clone,Distrotech/clutter,GNOME/clutter,GNOME/clutter,collects/clutter,ebassi/clutter,djdeath/clutter,collects/clutter