Prevent quit on immediate frontend in intercept mode

Otherwise we quit before the immediate frontend had a chance to start.
The immediate frontend will then automatically and unconditionally quit
once it's finished.

One thing that we can still improve is to hide the GUI in intercept mode
once an event was intercepted.

src/backend.cpp

@@ -167,7 +167,7 @@ void Backend::handle_dropped_urls(const QList<QUrl> &urls) {
 		Backend::get()->print_hyperlinks(paths);
 	}
 
-	if (Settings::get()->auto_quit_behavior == Settings::AutoQuitBehavior::First) {
+	if (Settings::get()->auto_quit_behavior == Settings::AutoQuitBehavior::First && Settings::get()->effective_frontend(true) != Settings::Frontend::Immediate) {
 		Backend::get()->quit_delayed();
 	}
 }