fix: potential null of .previous array

- fixed one rare case where .previous may be "null" instead of an empty array

src/structures/Queue.ts

@@ -39,7 +39,7 @@ export class Queue extends Array<Track> {
 	public current: Track | null = null;
 
 	/** The previous tracks */
-	public previous: Track[] | null = null;
+	public previous: Track[] = [];
 
 	/** The Manager instance. */
 	public manager: Manager;