Remove QML warning at startup

Using undefined works properly, but generates a warning. The other solution is to set the maximum size to something knowingly big.

CURA-10896

resources/qml/Cura.qml

@@ -826,8 +826,8 @@ UM.MainWindow
     {
         id: addMachineDialog
         title: catalog.i18nc("@title:window", "Add Printer")
-        maximumWidth: undefined
-        maximumHeight: undefined
+        maximumWidth: Screen.width * 2
+        maximumHeight: Screen.height * 2
         model: CuraApplication.getAddPrinterPagesModel()
         progressBarVisible: false
     }