#13 crash on dvdnav_next_pg_search(NULL);

[Jan-Willem]

if calling dvdnav_next_pg_search with a NULL pointer,
libdvdnav will crash because it tries to call printerr
("Passed a NULL pointer."); which will try to write an
error to NULL->err_str

dvdnav_status_t dvdnav_next_pg_search(dvdnav_t
this) {
vm_t try_vm;

if(!this) {
printerr("Passed a NULL pointer.");
return DVDNAV_STATUS_ERR;
}

....

not only dvdnav_next_pg_search suffers from this
problem, but most functions do

and yes, I know I should check the pointer first myself
for NULL, but I just came across this;