music.is_playing() appears to require an argument

[steam21]

Hi,
It would appear that music.is_playing() requires an argument. The argument is not mentioned in the documentation and in the source it appears to be ignored. If the intention is to be able to ask whether a particular music file is currently playing (which would be nice seeing as though you can queue multiple files) then can I suggest the argument is optional and if not passed means ANY music file is playing.

[lordmauve]

I think that is just a bug; it doesn't use the argument. We should remove it.