Clarification to suppress Coverity CID 405.

Every or conn has an outbuf, but coverity has no way of knowing that.
Add an assert to ease its conscience.

src/or/main.c

@@ -731,6 +731,7 @@ run_connection_housekeeping(int i, time_t now)
     return; /* we're all done here, the rest is just for OR conns */
 
   or_conn = TO_OR_CONN(conn);
+  tor_assert(conn->outbuf);
 
   if (or_conn->is_bad_for_new_circs && !or_conn->n_circuits) {
     /* It's bad for new circuits, and has no unmarked circuits on it: