FIX: disable the switch nozzle if not connected

jira: [STUDIO-10072]
Change-Id: I2f705af4cd6f50770c9c0019287855ef90518d18
(cherry picked from commit eae81e9d95059d6fef7dc0ee9e7c38f57e57e902)

src/slic3r/GUI/StatusPanel.cpp

@@ -2394,7 +2394,12 @@ bool StatusPanel::is_task_changed(MachineObject* obj)
 
 void StatusPanel::update(MachineObject *obj)
 {
-    if (!obj) return;
+    if (!obj)
+    {
+        m_nozzle_btn_panel->Disable();
+        return;
+    }
+
     //m_project_task_panel->Freeze();
     update_subtask(obj);
     //m_project_task_panel->Thaw();