Prevented foobar crash when exiting during AllMusic fetching

[TT-ReBORN]

As title says, more info here:
https://hydrogenaud.io/index.php/topic,121047.msg1044579.html#msg1044579

@regorxxx, you can close your open PR as it is with this PR deprecated: #7

[regorxxx]

Closed it.

@TT-ReBORN just to confirm, the current code handles only a single request at a time. Is that intended?
Just asking, as far as I see the previous one allowed to send multiple request when changing selection and processing them on the background via promises (correct me if I'm wrong, but at least that seems the flow).
Your PR is not only a fix but a change on behavior, since every send call aborts the previous request instead of pushing them into a stack and aborting the entire stack on the unload callback (which was my proposed solution).

[TT-ReBORN]

Yes, it should process single requests and start fresh again.
Imo this is the cleanest way and performance wise ( client <-> server side ), we do not need to have multiple request
processed because we only fetch text ( which is instant ) and no images like last.fm does.
I do not see any side effects, I have tested it with Majestyk and we didn't encounter any issues.