QuickTime chapter track ID increases by 1 on every import

[L2501]

QuickTime chapter track ID increases by 1 on every import

If you import the chapters multiple times it can get big

[enzo1982]

The current implementation of MP4File::SetChapters first deletes the existing chapter track and then adds a new one with the supplied chapters. This necessarily leads to the chapter track ID being changed, as explained in #41.

It may be possible to change the implementation of SetChapters to modify an existing chapter track instead of deleting it and adding a new one, but further investigation is needed.