fix #H172 - inconsistent damage calculation for negative AC

Reported last August by <email deleted>:  the code
that decided whether hero poly'd into a pudding would be split when being
hit by an iron weapon always reduced damage by u.uac if armor class is
negative, whereas the normal amount is -rnd(-u.uac).  So player pudding
with good armor always got maximum reduction.  Probably had little actual
effect on game play; puddings can't wear armor so would need to be using
rings and/or spell of protection and/or have eaten rings of protection
while in some previous metallivoric form in order to get good enough AC
for this to matter.

doc/fixes35.0

@@ -204,6 +204,8 @@ wielded bow shouldn't affect outcome of kicked arrows
 ranged polearm hit can divide puddings and can use confuse monster effect
 charge for kicked shop-owned food if it gets used up taming a monster
 give better feedback when thrown shop-owned food gets used up taming a monster
+effect of negative AC on damage received was calculated differently than
+	normal when deciding whether hero poly'd into pudding would split
 
 
 Platform- and/or Interface-Specific Fixes