protoboard: bail with error on peer overflow

It's probably better to just print an error instead of crashing the
entire framework if someone tries to create too many peers. There's just
too many places this can be triggered from.

src/libs/protoboard/blackboard_manager.cpp

@@ -120,6 +120,12 @@ BlackboardManager::get_blackboard()
 void
 BlackboardManager::add_peer(ProtobufPeerInterface *iface, long peer_id)
 {
+	if (next_peer_idx_ >= iface->maxlenof_peers()) {
+		logger->log_error(name(),
+		                  "Maximum number of peers reached. Can't create new peer with index %d!",
+		                  next_peer_idx_);
+		return;
+	}
 	iface->set_peers(next_peer_idx_++, peer_id);
 	iface->write();
 }