Fix the Empty backend

Sources/kha/graphics1/Graphics4.hx

@@ -6,10 +6,12 @@ import kha.Blob;
 import kha.Color;
 import kha.FastFloat;
 import kha.Image;
+import kha.graphics4.ComputeShader;
 import kha.graphics4.ConstantLocation;
 import kha.graphics4.IndexBuffer;
 import kha.graphics4.MipMapFilter;
 import kha.graphics4.PipelineState;
+import kha.graphics4.ShaderStorageBuffer;
 import kha.graphics4.TextureFilter;
 import kha.graphics4.TextureAddressing;
 import kha.graphics4.TextureUnit;
@@ -293,4 +295,16 @@ class Graphics4 implements kha.graphics4.Graphics {
 	public function maxBoundTextures(): Int {
 		return 16;
 	}
+
+	public function setShaderStorageBuffer(buffer: ShaderStorageBuffer, index: Int) {
+
+	}
+
+	public function setComputeShader(shader: ComputeShader) {
+
+	}
+
+	public function compute(x: Int, y: Int, z: Int) {
+
+	}
 }