Fix mixer channel updates on solo/mute

Fix the update of the mixer channels whenever a channel is soloed or muted.

The solution is rather "brutal" as it updates all mixer channel views when one of the models changes.

Introduce private helper method `MixerView::updateAllMixerChannels`. It calls the `update` method on each `MixerChannelView` so that they can get repainted.

Call `updateAllMixerChannels` at the end of the existing method `toggledSolo`.

Introduce a new method `MixerView::toggledMute` which is called whenever the mute model of a channel changes. It also updates all mixer channels.

Fixes #7054.

include/MixerView.h

@@ -98,6 +98,10 @@ protected:
 private slots:
 	void updateFaders();
 	void toggledSolo();
+	void toggledMute();
+
+private:
+	void updateAllMixerChannels();
 
 private:
 	QVector<MixerChannelView*> m_mixerChannelViews;

src/gui/MixerChannelView.cpp

@@ -104,6 +104,7 @@ namespace lmms::gui
         m_muteButton->setInactiveGraphic(embed::getIconPixmap("led_green"));
         m_muteButton->setCheckable(true);
         m_muteButton->setToolTip(tr("Mute this channel"));
+        connect(&mixerChannel->m_muteModel, &BoolModel::dataChanged, mixerView, &MixerView::toggledMute, Qt::DirectConnection);
 
         m_soloButton = new PixmapButton(this, tr("Solo"));
         m_soloButton->setModel(&mixerChannel->m_soloModel);

src/gui/MixerView.cpp

@@ -283,6 +283,22 @@ void MixerView::loadSettings(const QDomElement& domElement)
 void MixerView::toggledSolo()
 {
 	Engine::mixer()->toggledSolo();
+
+	updateAllMixerChannels();
+}
+
+
+void MixerView::toggledMute()
+{
+	updateAllMixerChannels();
+}
+
+void MixerView::updateAllMixerChannels()
+{
+	for (int i = 0; i < m_mixerChannelViews.size(); ++i)
+	{
+		m_mixerChannelViews[i]->update();
+	}
 }