Fix Null object Reference (#337)

* Fix Null object Reference

When you pause in a specific time in the countdown (when the countdown is finishing) it crashs.

I just added a null check for the song to fix it.

* Update PlayState.hx

source/funkin/game/PlayState.hx

@@ -1260,7 +1260,7 @@ class PlayState extends MusicBeatState
 				if (Conductor.songPosition >= 0)
 					startSong();
 			}
-		} else {
+		} else if (FlxG.sound.music != null) {
 			var instTime = FlxG.sound.music.time;
 			var isOffsync = vocals.time != instTime || [for(strumLine in strumLines.members) strumLine.vocals.time != instTime].contains(true);
 			__vocalOffsetViolation = Math.max(0, __vocalOffsetViolation + (isOffsync ? elapsed : -elapsed / 2));