Fix a bug with OpenVINO backend

modules/dnn/src/dnn.cpp

@@ -1899,6 +1899,9 @@ struct Net::Impl
                 }
             }
 
+            if (preferableBackend != DNN_BACKEND_OPENCV)
+                continue;  // Go to the next layer.
+
             // the optimization #2. if there is no layer that takes max pooling layer's computed
             // max indices (and only some semantical segmentation networks might need this;
             // many others only take the maximum values), then we switch the max pooling