Filip Roséen authored Mar 22, 2017 and Hugo Beauzée-Luyssen committed Mar 29, 2017

As we can have incoming requests to the preparser while we are
destroying libvlc, we can end up in a deadlock while we are removing
all playlist_item_t from the playlist, while an item being preparsed
tries to add additional items to the list.

These changes fixes the issue by introducing a preparser-deactivation
function, that will make sure that we:

 1) clear out any pending preparsing requests
 2) cancel the current item preparsing (blocking)
 3) prevent further requests to the preparser

fixes: #18151

Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>