input/var: fix deletion of seekpoint navigation callbacks
input/var: fix deletion of seekpoint navigation callbacks

The vlc-variables that will have their callbacks removed through
InputDelCallbacks related to seekpoint-navigation only exists if the
current title has more than one seekpoint.

This means that we would potentially try to remove callbacks from
variables that does not exist.

This fixes the issue by having symmetry between creation of the
callbacks (src/input/var.c:381-397), and deletion of such.

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

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc