Merge pull request #5153 from sebavan/master

Quick fix

src/Audio/babylon.sound.ts

@@ -574,12 +574,12 @@ module BABYLON {
                                         playPromise.catch(function(error) {
                                             // Automatic playback failed.
                                             // Waiting for the audio engine to be unlocked by user click on unmute
-                                            Engine.audioEngine.onAudioUnlockedObservable.addOnce(() => tryToPlay);
+                                            Engine.audioEngine.onAudioUnlockedObservable.addOnce(() => { tryToPlay(); });
                                         });
                                     }
                                 }
                                 else {
-                                    Engine.audioEngine.onAudioUnlockedObservable.addOnce(() => tryToPlay);
+                                    Engine.audioEngine.onAudioUnlockedObservable.addOnce(() => { tryToPlay(); });
                                 }
                             }
                             tryToPlay();