obs: Fix label in volume control

Use a dedicated method for setting the dB label in the volume control
and make sure to call it regardless if the volume was changed through
the slider or from somewhere else.

obs/volume-control.cpp

@@ -36,6 +36,7 @@ void VolControl::OBSVolumeLevel(void *data, calldata_t *calldata)
 void VolControl::VolumeChanged()
 {
 	slider->setValue((int) (obs_fader_get_deflection(obs_fader) * 100.0f));
+	updateText();
 }
 
 void VolControl::VolumeLevel(float mag, float peak, float peakHold)
@@ -46,6 +47,11 @@ void VolControl::VolumeLevel(float mag, float peak, float peakHold)
 void VolControl::SliderChanged(int vol)
 {
 	obs_fader_set_deflection(obs_fader, float(vol) * 0.01f);
+	updateText();
+}
+
+void VolControl::updateText()
+{
 	volLabel->setText(QString::number(obs_fader_get_db(obs_fader), 'f', 1)
 			.append(" dB"));
 }

obs/volume-control.hpp

@@ -44,6 +44,7 @@ private slots:
 	void VolumeChanged();
 	void VolumeLevel(float mag, float peak, float peakHold);
 	void SliderChanged(int vol);
+	void updateText();
 
 public:
 	VolControl(OBSSource source);