mpickobj sanity, ball&chain theft feedback

Something I've had sitting around for quite a while.  Add a sanity
check to mpickobj().  (It will need tweaking if b&c are changed to be
in engulfer's inventory.)

Also, include more information in the feedback when a nymph steals
attached iron ball:  "Nymph removed your chain and stole a heavy iron
ball".

And don't set the avenge-ok flag if uball is the item stolen since
thief was doing hero a favor, or for anything when the thief is under
the influence of Conflict.

src/steal.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	steal.c	$NHDT-Date: 1554580626 2019/04/06 19:57:06 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.72 $ */
+/* NetHack 3.6	steal.c	$NHDT-Date: 1561588404 2019/06/26 22:33:24 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.73 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2012. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -173,7 +173,7 @@ stealarm(VOID_ARGS)
             break;
         }
     }
-botm:
+ botm:
     stealoid = 0;
     return 0;
 }
@@ -249,7 +249,7 @@ char *objnambuf;
     struct obj *otmp;
     int tmp, could_petrify, armordelay, olddelay, named = 0, retrycnt = 0;
     boolean monkey_business, /* true iff an animal is doing the thievery */
-        was_doffing;
+            was_doffing, was_punished = Punished;
 
     if (objnambuf)
         *objnambuf = '\0';
@@ -264,7 +264,7 @@ char *objnambuf;
         (void) maybe_finished_meal(FALSE);
 
     if (!invent || (inv_cnt(FALSE) == 1 && uskin)) {
-    nothing_to_steal:
+ nothing_to_steal:
         /* Not even a thousand men in armor can strip a naked man. */
         if (Blind)
             pline("Somebody tries to rob you, but finds nothing to steal.");
@@ -285,7 +285,7 @@ char *objnambuf;
         goto gotobj;
     }
 
-retry:
+ retry:
     tmp = 0;
     for (otmp = invent; otmp; otmp = otmp->nobj)
         if ((!uarm || otmp != uarmc) && otmp != uskin
@@ -320,7 +320,7 @@ retry:
     else if (otmp == uarmu && uarm)
         otmp = uarm;
 
-gotobj:
+ gotobj:
     if (otmp->o_id == stealoid)
         return 0;
 
@@ -332,6 +332,7 @@ gotobj:
     /* animals can't overcome curse stickiness nor unlock chains */
     if (monkey_business) {
         boolean ostuck;
+
         /* is the player prevented from voluntarily giving up this item?
            (ignores loadstones; the !can_carry() check will catch those) */
         if (otmp == uball)
@@ -348,7 +349,7 @@ gotobj:
         if (ostuck || can_carry(mtmp, otmp) == 0) {
             static const char *const how[] = { "steal", "snatch", "grab",
                                                "take" };
-        cant_take:
+ cant_take:
             pline("%s tries to %s %s%s but gives up.", Monnam(mtmp),
                   how[rn2(SIZE(how))],
                   (otmp->owornmask & W_ARMOR) ? "your " : "",
@@ -443,23 +444,26 @@ gotobj:
             impossible("Tried to steal a strange worn thing. [%d]",
                        otmp->oclass);
         }
-    } else if (otmp->owornmask)
+    } else if (otmp->owornmask) /* weapon or ball&chain */
         remove_worn_item(otmp, TRUE);
 
     /* do this before removing it from inventory */
     if (objnambuf)
         Strcpy(objnambuf, yname(otmp));
-    /* set mavenge bit so knights won't suffer an
+    /* usually set mavenge bit so knights won't suffer an alignment penalty
-     * alignment penalty during retaliation;
+       during retaliation; not applicable for removing attached iron ball */
-     */
+    if (!Conflict && !(was_punished && !Punished))
-    mtmp->mavenge = 1;
+        mtmp->mavenge = 1;
 
     if (otmp->unpaid)
         subfrombill(otmp, shop_keeper(*u.ushops));
     freeinv(otmp);
-    pline("%s stole %s.", named ? "She" : Monnam(mtmp), doname(otmp));
+    /* if attached ball was taken, uball and uchain are now Null */
-    could_petrify =
+    pline("%s%s stole %s.", named ? "She" : Monnam(mtmp),
-        (otmp->otyp == CORPSE && touch_petrifies(&mons[otmp->corpsenm]));
+          (was_punished && !Punished) ? " removed your chain and" : "",
+          doname(otmp));
+    could_petrify = (otmp->otyp == CORPSE
+                     && touch_petrifies(&mons[otmp->corpsenm]));
     (void) mpickobj(mtmp, otmp); /* may free otmp */
     if (could_petrify && !(mtmp->misc_worn_check & W_ARMG)) {
         minstapetrify(mtmp, TRUE);
@@ -477,6 +481,16 @@ register struct obj *otmp;
     int freed_otmp;
     boolean snuff_otmp = FALSE;
 
+    if (!otmp) {
+        impossible("monster (%s) taking or picking up nothing?",
+                   mtmp->data->mname);
+        return 1;
+    } else if (otmp == uball || otmp == uchain) {
+        impossible("monster (%s) taking or picking up attached %s (%s)?",
+                   mtmp->data->mname,
+                   (otmp == uchain) ? "chain" : "ball", simpleonames(otmp));
+        return 0;
+    }
     /* if monster is acquiring a thrown or kicked object, the throwing
        or kicking code shouldn't continue to track and place it */
     if (otmp == thrownobj)