fix: index check on triangle batch flush

Engine.Integration/Engine.Integration.MonoGame/TriangleBatch.cs

@@ -58,6 +58,9 @@ public class TriangleBatch : ITriangleBatch
 
     private void Flush()
     {
+        if (verticesIndex == 0)
+            return;
+
         graphicsDevice.RasterizerState = rasterizerState;
         basicEffect.Projection = _projection;
         basicEffect.View = _view;