Lesson 1: Drumkit - Playing multiple audios at once causes overlapping

[ItsNamrathaB]

We might not observe the issue with the existing audio files as they're small in length, but if we replace and play any existing audio with a bit longer one(suggested>~2-3s) and play another audio before this ends - it's causing an overlapped playing of both the audios.

Hence I added a fix to check if there's an existing audio play and pause it in the affirmative