Metal fixes

base/shaders/copy_mrt3_pass.kong

@@ -1,4 +1,9 @@
 
+#[set(everything)]
+const constants: {
+	empty: float4;
+};
+
 #[set(everything)]
 const sampler_linear: sampler;
 

base/shaders/copy_pass.kong

@@ -1,4 +1,9 @@
 
+#[set(everything)]
+const constants: {
+	empty: float4;
+};
+
 #[set(everything)]
 const sampler_linear: sampler;
 

base/shaders/histogram_pass.kong

@@ -1,4 +1,9 @@
 
+#[set(everything)]
+const constants: {
+	empty: float4;
+};
+
 #[set(everything)]
 const sampler_linear: sampler;
 

base/shaders/mask_apply.kong

@@ -1,4 +1,9 @@
 
+#[set(everything)]
+const constants: {
+	empty: float4;
+};
+
 #[set(everything)]
 const sampler_linear: sampler;