sendme: Fix coverity CID 1445000
Doesn't seems very good but at least not released ;).
*** CID 1445000: Null pointer dereferences (FORWARD_NULL)
/src/core/or/relay.c: 1952 in connection_edge_process_relay_cell()
1946 log_info(domain,
1947 "'connected' received on circid %u for streamid %d, "
1948 "no conn attached anymore. Ignoring.",
1949 (unsigned)circ->n_circ_id, rh.stream_id);
1950 return 0;
1951 case RELAY_COMMAND_SENDME:
>>> CID 1445000: Null pointer dereferences (FORWARD_NULL)
>>> Passing null pointer "layer_hint" to "process_sendme_cell", which dereferences it.
1952 return process_sendme_cell(&rh, cell, circ, conn, layer_hint, domain);
1953 case RELAY_COMMAND_RESOLVE:
1954 if (layer_hint) {
1955 log_fn(LOG_PROTOCOL_WARN, LD_APP,
1956 "resolve request unsupported at AP; dropping.");
1957 return 0;