Fix stroke mesh multiple release issue.

Runtime/ui/renderer/cmdbufferCanvas/rendering/canvas_impl.cs

 
             if (strokeMesh != null) {
                 layer.draws.Add(CanvasShader.strokeAlpha(layer, p, alpha, strokeMult, strokeMesh));
-                layer.draws.Add(CanvasShader.stroke1(layer, strokeMesh));
+                layer.draws.Add(CanvasShader.stroke1(layer, strokeMesh.duplicate()));
             }
         }