Add early return for zero duration sounds (source-academy#932)

* Add early return for zero duration sounds

* Change guard clause to include all non-positive durations

Author: iskandarzulkarnaien

public/externalLibs/sound/sounds.js

@@ -202,6 +202,8 @@ function play_unsafe(sound) {
     // If a sound is already playing, terminate execution
     } else if (_playing || _safeplaying) {
         throw new Error("play: audio system still playing previous sound");
+    } else if (get_duration(sound) <= 0) {
+        return sound;
     } else {
         // Declaring duration and wave variables
         var wave = get_wave(sound);
@@ -308,6 +310,8 @@ function play(sound) {
     // If a sound is already playing, terminate execution.
     if (_safeplaying || _playing) {
         throw new Error("play: audio system still playing previous sound");
+    } else if (get_duration(sound) <= 0) {
+        return sound;
     } else {
         // Discretize the input sound
         var data = discretize(get_wave(sound), get_duration(sound));