undo minor change

src/Math/babylon.math.ts

@@ -5667,7 +5667,7 @@ module BABYLON {
          */
         public static OrthoOffCenterRHToRef(left: number, right: number, bottom: number, top: number, znear: number, zfar: number, result: Matrix): void {
             Matrix.OrthoOffCenterLHToRef(left, right, bottom, top, znear, zfar, result);
-            result.multiplyAtIndex(10, -1);
+            result._m[10] *= -1; // No need to call _markAsUpdated as previous function already called it and let _isIdentityDirty to true
         }
 
         /**