alib2gui: Fix build on debian:testing

alib2gui/src/MainWindow.cpp

@@ -265,9 +265,9 @@ void MainWindow::on_actionSave_triggered() {
                         std::find(allBoxes.begin(), allBoxes.end(), conn->getTargetConnectionBox()->getParent()) -
                         allBoxes.begin();
                 Json::Value connection;
-                connection["from"] = i;
-                connection["to"] = targetIndex;
-                connection["slot"] = conn->getTargetConnectionBox()->getSlot();
+                connection["from"] = Json::Value::UInt64(i); /* cast to UInt64 for debian compatibility, see https://github.com/open-source-parsers/jsoncpp/issues/403 */
+                connection["to"] = Json::Value::UInt64(targetIndex); /* same */
+                connection["slot"] = Json::Value::UInt64(conn->getTargetConnectionBox()->getSlot()); /* same */
                 connections.append(connection);
             }
         }