recursive=expand can be too time-consuming (preventing users from exiting vlc)

We do not need to copy here anyway.

This kills a memory copy in most cases (FFMPEG input padding is the same
as VLC block padding, at least on my system).

is found (same function but not same data).
This can be usefull to find some errors.
This is only activated in debug mode.

 * Shrink the buffer in either direction before reallocating,
   so we don't need to copy discarded data.
(* Special case if the payload is entirely discarded.)
 * Avoid potentially overflowing pointer comparisons
  (In real life, it works, but it is not defined by the C specification).

And remove a lot of unnecessary code.

Basically, we starting scrolling at the beginning, if the window gets reopened and jump back to top once scrolling reached the end of the list.