playlist: repair playlist order on shuffle (fix #4857)
playlist: repair playlist order on shuffle (fix #4857)

Selecting first item to play in random mode as null, the old method
was giving a random item at a random position which resulted in only a
part of the queue playing. If we set first item to NULL, playlist
automaticaly selects first item from the reshuffled queue in the
request processing loop.

Signed-off-by: Jean-Baptiste Kempf <7b85a41a628204b76aba4326273a3ccc74bd009a@videolan.org>

vlc-mirror/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,xkfz007/vlc,shyamalschandra/vlc,shyamalschandra/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,krichter722/vlc,shyamalschandra/vlc