Fix V803 Decreased performance. In case 'it' is iterator it's more effective to use prefix form of increment.

Replace iterator++ with ++iterator. stream_engine.cpp
    http://www.viva64.com/en/d/0165/print/

src/stream_engine.cpp

@@ -781,7 +781,7 @@ void zmq::stream_engine_t::mechanism_ready ()
     it = zap_properties.begin ();
     while (it != zap_properties.end ()) {
         properties.insert (properties_t::value_type (it->first, it->second));
-        it++;
+        ++it;
     }
 
     //  Add ZMTP properties.
@@ -789,7 +789,7 @@ void zmq::stream_engine_t::mechanism_ready ()
     it = zmtp_properties.begin ();
     while (it != zmtp_properties.end ()) {
         properties.insert (properties_t::value_type (it->first, it->second));
-        it++;
+        ++it;
     }
 
     zmq_assert (metadata == NULL);