Change from the previous version: by default, the current behaviour
of the decoder is preserved. Samples to skip are zero by default.
We can improve this later.

For some reason, this was never set, which meant all **raw** AAC in ADTS
streams, except faac, had extra samples at the start.

Despite this being a standard MDCT-based codec with a frame size of 1024,
hence a delay of 1024 samples at the start, all major encoders, excluding
faac and ffmpeg, use different amounts of padding.

Patch attached.