node.cpp: Fix possible race condition in process_backlog_of_sync_bloc…

…ks() #1434

libraries/net/node.cpp

@@ -3303,6 +3303,7 @@ namespace graphene { namespace net { namespace detail {
             else
             {
               dlog("Already received and accepted this block (presumably through normal inventory mechanism), treating it as accepted");
+              std::vector< peer_connection_ptr > peers_needing_next_batch;
               for (const peer_connection_ptr& peer : _active_connections)
               {
                 auto items_being_processed_iter = peer->ids_of_items_being_processed.find(received_block_iter->block_id);
@@ -3320,10 +3321,12 @@ namespace graphene { namespace net { namespace detail {
                       peer->ids_of_items_being_processed.empty())
                   {
                     dlog("We received last item in our list for peer ${endpoint}, setup to do a sync check", ("endpoint", peer->get_remote_endpoint()));
-                    fetch_next_batch_of_item_ids_from_peer(peer.get());
+                    peers_needing_next_batch.push_back( peer );
                   }
                 }
               }
+              for( const peer_connection_ptr& peer : peers_needing_next_batch )
+                fetch_next_batch_of_item_ids_from_peer(peer.get());
             }
 
             break; // start iterating _received_sync_items from the beginning