This change affects cases where a sound is loaded while the same sound
is still in the process of being decoded. It makes it so the ASYNC flag
will only wait for the underlying data buffer to be initialized,
whereas the lack of ASYNC flag will result in it waiting for the entire
sound to be fully decoded.

This is locked behind the following compile time macro for now since
it'll involve breaking changes to custom data sources. This will be
removed in version 0.11:

  MA_EXPERIMENTAL__DATA_LOOPING_AND_CHAINING

Public issue https://github.com/mackron/miniaudio/issues/290

Public issue https://github.com/mackron/miniaudio/pull/308

Public issue https://github.com/mackron/miniaudio/issues/290

This only works for non-streaming sounds whose data source was created
via the resource manager.

Public issue https://github.com/mackron/miniaudio/issues/291