Fix zero-end in shallow slice

[dy]

For the case

bl.shallowSlice(0, 0)

bl returns full buffer, which seems to be wrong. So here is the fix.
Is there any sense in making bl.shallowSlice(0, -0)?

[dy]

I guess you may want tests?

[dy]

Oh no, it's broken

[mcollina]

I'm on vacation for the next two weeks, I will release when I come back.

[dy]

Hm. Seems that here it will also break on single-buffer operation, like bl(Buffer('abcdef')).slice(2,4). Should cover that too (gotcha from audio-buffer-list)

[mcollina]

Check version v1.2.1, #44 might fix your bug.