Fix wrong bitwise shift operation.

Close #2279.

Source/Urho3D/Urho2D/Drawable2D.h

@@ -106,7 +106,7 @@ protected:
     virtual void UpdateSourceBatches() = 0;
 
     /// Return draw order by layer and order in layer.
-    int GetDrawOrder() const { return (layer_ << 20) + (orderInLayer_ << 10); }
+    int GetDrawOrder() const { return layer_ << 16u | orderInLayer_; }
 
     /// Layer.
     int layer_;