Fix Per Object Settings toolbutton enabled state on startup

Contributes to CURA-901

plugins/PerObjectSettingsTool/PerObjectSettingsTool.py

@@ -16,6 +16,7 @@ class PerObjectSettingsTool(Tool):
 
         self.setExposedProperties("Model", "SelectedIndex")
 
+        Application.getInstance().getController().toolEnabledStateRequest.connect(self._onToolEnabledStateRequested)
         Preferences.getInstance().preferenceChanged.connect(self._onPreferenceChanged)
 
     def event(self, event):
@@ -40,6 +41,9 @@ class PerObjectSettingsTool(Tool):
         index = self.getModel().find("id", selected_object_id)
         return index
 
+    def _onToolEnabledStateRequested(self):
+        self._onPreferenceChanged("cura/active_mode")
+
     def _onPreferenceChanged(self, preference):
         if preference == "cura/active_mode":
             enabled = Preferences.getInstance().getValue(preference)==1