Previously, MPD would skip the current song after attempting to seek
to its beginnig, because that was a seek to offset 0. At offset 0,
MPD will see the BOS packet again, which results in throwing
StopDecoder in MPDOpusDecoder::OnOggEnd().
Closes https://github.com/MusicPlayerDaemon/MPD/issues/470
Since we switched from autotools to Meson in commit
94592c1406, we don't need to include
`config.h` early to properly enable large file support. Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.
This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.
