app-layer: increment flow counter if one sided

In the case of protocol like SMTP, we detect application layer on
only one side.  Consequence was a missed increment in the flow
counter.

src/app-layer.c

@@ -498,6 +498,7 @@ static int TCPProtoDetect(ThreadVars *tv,
                 TcpSessionSetReassemblyDepth(ssn,
                         AppLayerParserGetStreamDepth(f));
                 *alproto = ALPROTO_FAILED;
+                AppLayerIncFlowCounter(tv, f);
                 FlagPacketFlow(p, f, flags);
 
                 SCLogDebug("packet %u: pd done(us %u them %u), parser called (r==%d), APPLAYER_DETECT_PROTOCOL_ONLY_ONE_DIRECTION set",