Early cop-out if there is no printer connected

This indeterminate state is never visible, since showProgress is false then, but it might prevent some error message behind the scenes.

Contributes to issue CURA-2060.

resources/qml/MonitorButton.qml

@@ -161,6 +161,10 @@ Rectangle
         visible: showProgress;
         indeterminate:
         {
+            if (!printerConnected)
+            {
+                return true;
+            }
             switch(Cura.MachineManager.printerOutputDevices[0].jobState)
             {
                 case "pausing":