Fix error in Skybox.hlsl when instancing is forced on.

bin/CoreData/Shaders/HLSL/Skybox.hlsl

@@ -3,6 +3,9 @@
 #include "Transform.hlsl"
 
 void VS(float4 iPos : POSITION,
+    #ifdef INSTANCED
+        float4x3 iModelInstance : TEXCOORD4,
+    #endif
     out float3 oTexCoord : TEXCOORD0,
     out float4 oPos : OUTPOSITION)
 {