Add check preventing restarting the same audio resource. (#2002)

* Add check preventing restarting the same audio resource.

* Fix docs.

* Move resource check to the Audio subsystem.

addons/dialogic/Modules/Audio/event_music.gd

@@ -1,9 +1,9 @@
 @tool
+## Event that can change the currently playing background music.
+## This event won't play new music if it's already playing.
 class_name DialogicMusicEvent
 extends DialogicEvent
 
-## Event that can change the currently playing background music.
-
 
 ### Settings
 
@@ -24,9 +24,10 @@ var loop: bool = true
 ################################################################################
 
 func _execute() -> void:
-	dialogic.Audio.update_music(file_path, volume, audio_bus, fade_length, loop)
-	finish()
+	if not dialogic.Audio.is_music_playing_resource():
+		dialogic.Audio.update_music(file_path, volume, audio_bus, fade_length, loop)
 
+	finish()
 
 ################################################################################
 ## 						INITIALIZE
@@ -66,7 +67,7 @@ func get_shortcode_parameters() -> Dictionary:
 ## 						EDITOR REPRESENTATION
 ################################################################################
 
-func build_event_editor():
+func build_event_editor() -> void:
 	add_header_edit('file_path', ValueType.FILE, {
 			'left_text'		: 'Play',
 			'file_filter' 	: "*.mp3, *.ogg, *.wav; Supported Audio Files",

addons/dialogic/Modules/Audio/subsystem_audio.gd

@@ -112,5 +112,15 @@ func stop_all_sounds() -> void:
 		if "Sound" in node.name:
 			node.queue_free()
 
+
 func interpolate_volume_linearly(value :float, node:Node) -> void:
 	node.volume_db = linear_to_db(value)
+
+
+## Returns whether the currently playing audio resource is the same as this
+## event's [param resource_path].
+func is_music_playing_resource(resource_path: String) -> bool:
+	var is_playing_resource: bool = (base_music_player.is_playing()
+		and base_music_player.stream.resource_path == resource_path)
+
+	return is_playing_resource