Merge branch 'master' of github.com:Ultimaker/Cura

cura/MachineManagerModel.py

@@ -213,7 +213,7 @@ class MachineManagerModel(QObject):
     #   Calling _checkStackForErrors on every change is simply too expensive
     @pyqtProperty(bool, notify = globalValidationChanged)
     def isGlobalStackValid(self):
-        return self._global_stack_valid
+        return bool(self._global_stack_valid)
 
     @pyqtProperty(str, notify = activeStackChanged)
     def activeUserProfileId(self):

resources/qml/MonitorButton.qml

@@ -109,7 +109,7 @@ Rectangle
         id: abortButton
 
         visible: printerConnected
-        enabled: Cura.MachineManager.printerOutputDevices[0].jobState == "paused" || Cura.MachineManager.printerOutputDevices[0].jobState == "printing"
+        enabled: printerConnected && Cura.MachineManager.printerOutputDevices[0].jobState == "paused" || Cura.MachineManager.printerOutputDevices[0].jobState == "printing"
 
         height: UM.Theme.getSize("save_button_save_to_button").height
         anchors.top: progressBar.bottom
@@ -156,7 +156,7 @@ Rectangle
         id: pauseButton
 
         visible: printerConnected
-        enabled: Cura.MachineManager.printerOutputDevices[0].jobState == "paused" || Cura.MachineManager.printerOutputDevices[0].jobState == "printing"
+        enabled: printerConnected && Cura.MachineManager.printerOutputDevices[0].jobState == "paused" || Cura.MachineManager.printerOutputDevices[0].jobState == "printing"
 
         height: UM.Theme.getSize("save_button_save_to_button").height
         anchors.top: progressBar.bottom