Ensure we don't exit successfully if the main loop exits

We never quit the main loop, but if something odd happens that causes it
to quit outside our control, ensure that we don't return the "auth
success" status code.

dialog-gtk3/src/main.rs

@@ -324,8 +324,7 @@ fn main() -> anyhow::Result<()> {
     dialog.show_all();
 
     gtk::main();
-
+    DialogExitStatus::OtherError.exit();  // We should never get here!
-    Ok(())
 }
 
 fn set_time_label(label: &gtk::Label) {