Add Position and Len for flac

[cswank]

d.stream.Info.NSamples is uint64 so calling
int() on it could result in an overflow. I
have no idea how likely that is, but if it happens
then Position() will return -1.

I also don't know if this PR is the intent behind the beep.StreamSeeker interface, but it's working great for the app that I built using beep.

[faiface]

Cool, thanks! @mewmew, can you confirm this is correct?

[cswank]

I think it might not be 100% correct. The songs I've been playing never get to Len(). Position() seems to stop short each time.

[cswank]

I think I fixed it with the 2nd commit: update d.pos on EOF error.

[mewmew]

Cool, thanks! @mewmew, can you confirm this is correct?

Looks correct from what I can tell. Good job @cswank :) Now there is only one method left to implement! Seek.

For reference to anyone feeling brave enough, the upsteam issue tracking the implementation of seek for FLAC files is mewkiz/flac#16. It's up for grabs.

[cswank]

My app would benefit from Seek. I'll take a look and see how brave I feel after some reading.

[mewmew]

My app would benefit from Seek. I'll take a look and see how brave I feel after some reading.

That's great to hear! Preemptively, I've started writing a hymn that will be sung around campfires for generations to come. ♩♪♬♩

[cswank]

Hey @faiface, this is a friendly reminder that this PR should be good to go.

[faiface]

Oh, sorry, I forgot :) Here we go