Fix a bug in saving model with mesh where mesh name was modified

When saving a model with mesh, the mesh collection's name was modified to "no mesh". The problem is that during serialization of operator result, we check whether the writeLocation of the collection is empty, if not, we will write out the mesh to a file at write location. But after that, we should have set the writeLocation of the collection to empty, otherwise any other operations will go through the same logic while serializing operator result, and the mesh will be re-written.