Add a missing return after marking a stream for bad connected cell

Fixes bug 26072; bugfix on 0.2.4.7-alpha.

changes/bug26072

+  o Minor bugfixes (correctness, client):
+    - Upon receiving a malformed connected cell, stop processing the cell
+      immediately.  Previously we would mark the connection for close, but
+      continue processing the cell as if the connection were open. Fixes bug
+      26072; bugfix on 0.2.4.7-alpha.

src/or/relay.c

@@ -1323,6 +1323,7 @@ connection_edge_process_relay_cell_not_open(
              "Got a badly formatted connected cell. Closing.");
       connection_edge_end(conn, END_STREAM_REASON_TORPROTOCOL);
       connection_mark_unattached_ap(entry_conn, END_STREAM_REASON_TORPROTOCOL);
+      return 0;
     }
     if (tor_addr_family(&addr) != AF_UNSPEC) {
       const sa_family_t family = tor_addr_family(&addr);