Fix: double Bell of Opening in Val and Arc quests

This is the result of the fix in 2d4f989 that makes a nemesis who's
about to receive lua-specified inventory drop any special items they may
have already received. In the commit note there I even noted two Bells
could generate if a level developer specified the nemesis gets the Bell
and fails to specify keep_default_invent = true, but also noted that
"two Bells is better than none", which it is - the player who reported
this wasn't facing an unwinnable situation.

Specifying keep_default_invent = true as I did here was not necessary to
fix the two-Bells issue, but does address another problem: that the
default behavior when keep_default_invent is false is to *drop* special
items, meaning the nemesis would either abandon the Bell on the floor or
waste turns warping back to pick it up once they moved off. I considered
doing a more comprehensive fix that would keep the special items in the
nemesis's inventory, but decided not to since it would duplicate code
from mdrop_special_objs.

Author: copperwater

dat/Arc-goal.lua

@@ -90,8 +90,10 @@ des.monster({ id="Schliemann", x=53, y=09, inventory = function()
    -- nethack doesn't have explosives; this is the closest substitute...
    des.object({ id="oil", cursed=0, quantity=7+d(5) })
    des.object({ id="shield of reflection",buc="blessed",material="gold",spe=1,name="Itlachiayaque" })
-   des.object({ id="Bell of Opening", buc="uncursed" })
-end })
+   -- bell of opening has hardcoded safeguards so specifying it here would
+   -- result in two bells; specify keep_default_invent=true so he is carrying it
+   -- rather than has dropped it
+end, keep_default_invent = true })
 
 -- His crew of archeologists
 function henchman_inventory()

dat/Val-goal.lua

@@ -96,8 +96,10 @@ end
 des.monster({ id='Lord Surtur', x=66, y=13, waiting=true, inventory=function()
    des.object({ id='two-handed sword', name='Sol Valtiva' })
    des.object({ class='/', id='fire', buc='not-cursed' })
-   des.object({ id='Bell of Opening', buc='uncursed' })
-end })
+   -- bell of opening has hardcoded safeguards so specifying it here would
+   -- result in two bells; specify keep_default_invent=true so he is carrying it
+   -- rather than has dropped it
+end, keep_default_invent = true })
 
 -- Other monsters
 for i = 1, 6 + d(4) do