gsturi: When setting the same string again do nothing
Otherwise code like gst_uri_set_host(uri, gst_uri_get_host(uri)) would first free the string, then create a copy of the freed string and then assigned that.
Otherwise code like gst_uri_set_host(uri, gst_uri_get_host(uri)) would first free the string, then create a copy of the freed string and then assigned that.