Send HTTP 200 in response to `Range: bytes=0-`

Ug, well, that's a pain.

It turns out that Chrome refuses to play audio if it gets an HTTP 206 in response to a request for `Range: bytes=0-`.

Chrome is kind of a jerk.

Anyway, since it isn't unreasonable to only return an HTTP 206 when the response is a proper subrange of the file, I've fixed things up so an HTTP 200 is returned if a `Range` is requested and that range is the complete file.