isisd: fix an error that was probably a result of copypasting

The code should check for the existance of the correct list prior to
accessing it.

Signed-off-by: Christian Franke <chris@opensourcerouting.org>
Signed-off-by: Christian Franke <chris@opensourcerouting.org>
Acked-by: Donald Sharp <sharpd@cumulusnetworks.com>
1 file changed