Fixing concurrency issue in rep.cpp resulting in broken connections with…

Fixing concurrency issue in rep.cpp resulting in broken connections with multiple requesters under heavy load.

src/rep.cpp

@@ -178,14 +178,15 @@ int zmq::rep_t::xrecv (zmq_msg_t *msg_, int flags_)
     //  Round-robin over the pipes to get next message.
     for (int count = active; count != 0; count--) {
         bool fetched = in_pipes [current]->read (msg_);
-        current++;
-        if (current >= active)
-            current = 0;
         if (fetched) {
             reply_pipe = out_pipes [current];
             waiting_for_reply = true;
-            return 0;
         }
+        current++;
+        if (current >= active)
+            current = 0;
+        if (fetched)
+            return 0;
     }
 
     //  No message is available. Initialise the output parameter