Yuck.  Instead of adding this extra parameter, the damage should be bounded in the caller (in this case, wallfire.kod and walltng.kod, or possibly their parent class if there's a clean way to do it).  This is a general principle: prefer to put knowledge (in this case, "wall spells can't kill you") in the class that owns the behavior (in this case, wall spells) rather than the target (in this case, player).

If this is put in the wall spells, it would have the side effect that monsters could also not be killed by wall spells.  I like this as a counter to the bait + firewall "strategy".