AudioApplet: Update the volume slider on update from audio server

Author: https://github.com/Granddave
Commit: c1458e8061
Pull-request: https://github.com/SerenityOS/serenity/pull/10119
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Applets/Audio/main.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ * Copyright (c) 2021, David Isaksson <davidisaksson93@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -40,6 +41,7 @@ public:
 
         m_audio_client->on_main_mix_volume_change = [this](double volume) {
             m_audio_volume = static_cast<int>(volume * 100);
+            m_slider->set_value(m_slider->max() - m_audio_volume, GUI::CallOnChange::No);
             if (!m_audio_muted)
                 update();
         };