macOS: make mute sound actually work (#15128)

src/client/sound/sound_manager.cpp

@@ -29,6 +29,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "filesys.h"
 #include "porting.h"
 
+#include <limits>
+
 namespace sound {
 
 void OpenALSoundManager::stepStreams(f32 dtime)
@@ -347,6 +349,13 @@ void OpenALSoundManager::updateListener(const v3f &pos_, const v3f &vel_,
 
 void OpenALSoundManager::setListenerGain(f32 gain)
 {
+#if defined(__APPLE__)
+	/* macOS OpenAL implementation ignore setting AL_GAIN to zero
+	 * so we use smallest possible value
+	 */
+	if (gain == 0.0f)
+		gain = std::numeric_limits<f32>::min();
+#endif
 	alListenerf(AL_GAIN, gain);
 }