rpcrt4: Fix potential NULL pointer access in process_bind_packet.

Upon failure to allocate results in process_bind_packet, build nack
packet and send right away, instead of falling into the normal path
and potentially dereferencing the NULL pointer.

dlls/rpcrt4/rpc_server.c

@@ -203,6 +203,7 @@ static RPC_STATUS process_bind_packet(RpcConnection *conn, RpcPktBindHdr *hdr, R
         response = RPCRT4_BuildBindNackHeader(NDR_LOCAL_DATA_REPRESENTATION,
                                               RPC_VER_MAJOR, RPC_VER_MINOR,
                                               REJECT_LOCAL_LIMIT_EXCEEDED);
+        goto send;
     }
 
     for (i = 0, ctxt_elem = (RpcContextElement *)msg->Buffer;