Fix #185

[NycroV]

Fixes the issue described in #185

We don't need to use the null check operator, as the result will always be null before assigning.
Document that the returned index is the index of the last track added to the queue if a playlist is passed, not the first.

Ex: queueing 5 tracks on a player that is currently playing, but has an empty queue, should return 5.

[github-actions]

Delta Summary

Generated on:	09/23/2024 - 03:46
Description	Previous	Current	Delta
Coverage date:	09/12/2024 - 18:05	09/23/2024 - 03:46
Line coverage:	64.5%	66.4%	1.9%
Covered lines:	17818	14694	-3124
Coverable lines:	27584	22106	-5478
Total lines:	60678	60595	-83
Branch coverage:	50.2%	51.2%	1.0%
Covered branches:	2534	2512	-22
Total branches:	5045	4901	-144
Method coverage:	Feature is only available for sponsors

[NycroV]

Oops, renamed the branch to be more in-line with existing branch naming, and it closed the PR.
Will re-open momentarily.