implement wlr-gamma-control-unstable-v1

src/backends/x.rs

@@ -493,6 +493,7 @@ impl XBackend {
             format: FORMAT,
             color_space: Default::default(),
             eotf: Default::default(),
+            gamma_lut: Default::default(),
         };
         let output = Rc::new(XOutput {
             id: self.state.connector_ids.next(),