stream: fix reachable assertion

Fix `Flow::thread_id` not always getting properly set up, leading to
a reachable assertion.

Bug #4582.

src/stream-tcp.c

@@ -4941,8 +4941,6 @@ int StreamTcpPacket (ThreadVars *tv, Packet *p, StreamTcpThread *stt,
 
     SCLogDebug("p->pcap_cnt %"PRIu64, p->pcap_cnt);
 
-    HandleThreadId(tv, p, stt);
-
     TcpSession *ssn = (TcpSession *)p->flow->protoctx;
 
     /* track TCP flags */
@@ -5365,6 +5363,8 @@ TmEcode StreamTcp (ThreadVars *tv, Packet *p, void *data, PacketQueueNoLock *pq)
         return TM_ECODE_OK;
     }
 
+    HandleThreadId(tv, p, stt);
+
     /* only TCP packets with a flow from here */
 
     if (!(p->flags & PKT_PSEUDO_STREAM_END)) {