[BUG] config: fix wrong handling of too large argument count

[BUG] config: fix wrong handling of too large argument count

Holger Just reported that running ACLs with too many args caused
a segfault during config parsing. This is caused by a wrong test
on argument count. In case of too many arguments on a config line,
the last one was not correctly zeroed. This is now done and we
report the error indicating what part had been truncated.