cryptonote_protocol: fix out of order addition

This was broken by the reorg fix, since we now have to add blocks
regardless of their starting height. We now check whether we know
the parent for the first block in the next span, or whether it was
requested. If neither, it's an orphan. If it is not known, but was
requested, we wait to get that block.

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -990,6 +990,43 @@ namespace cryptonote
           MDEBUG(context << " next span in the queue has blocks " << start_height << "-" << (start_height + blocks.size() - 1)
               << ", we need " << previous_height);
 
+
+          block new_block;
+          if (!parse_and_validate_block_from_blob(blocks.front().block, new_block))
+          {
+            MERROR("Failed to parse block, but it should already have been parsed");
+            break;
+          }
+          bool parent_known = m_core.have_block(new_block.prev_id);
+          if (!parent_known)
+          {
+            // it could be:
+            //  - later in the current chain
+            //  - later in an alt chain
+            //  - orphan
+            // if it was requested, then it'll be resolved later, otherwise it's an orphan
+            bool parent_requested = false;
+	    m_p2p->for_each_connection([&](cryptonote_connection_context& context, nodetool::peerid_type peer_id, uint32_t support_flags)->bool{
+	      if (context.m_requested_objects.find(new_block.prev_id) != context.m_requested_objects.end())
+              {
+                parent_requested = true;
+                return false;
+              }
+	      return true;
+	    });
+            if (!parent_requested)
+            {
+              LOG_ERROR_CCONTEXT("Got block with unknown parent which was not requested - dropping connection");
+              // in case the peer had dropped beforehand, remove the span anyway so other threads can wake up and get it
+              m_block_queue.remove_spans(span_connection_id, start_height);
+              return 1;
+            }
+
+            // parent was requested, so we wait for it to be retrieved
+            MINFO(context << " parent was requested, we'll get back to it");
+            break;
+          }
+
           const boost::posix_time::ptime start = boost::posix_time::microsec_clock::universal_time();
 
           m_core.prepare_handle_incoming_blocks(blocks);