crash fix: shopkeeper re-entering shop

- when a shopkeeper leaves the shop to chase the player, and the player
enters the shop, bill_p is set to an unusual value.  bill_p needs to be set
back to a valid value if the shopkeeper re-enters the shop.
- Also, the u.ushops state needs to be updated when a shop becomes tended
again if the player is in the shop.
- introduce a new after_shk_move function to handle this

doc/fixes34.1

@@ -72,6 +72,7 @@ travel command should restrict its shortest paths to areas of the map the
 non-altar prayer should limit god action, not maximize it
 potions of acid explode, not dilute, so make water_damage behave this way
 lookat monster notes if you see monster is trapped
+don't crash when angry shopkeeper re-enters the shop and you pick up something
 
 
 Platform- and/or Interface-Specific Fixes

include/extern.h

@@ -1761,6 +1761,7 @@ E struct monst *FDECL(shkcatch, (struct obj *,XCHAR_P,XCHAR_P));
 E void FDECL(add_damage, (XCHAR_P,XCHAR_P,long));
 E int FDECL(repair_damage, (struct monst *,struct damage *,BOOLEAN_P));
 E int FDECL(shk_move, (struct monst *));
+E void FDECL(after_shk_move, (struct monst *));
 E boolean FDECL(is_fshk, (struct monst *));
 E void FDECL(shopdig, (int));
 E void FDECL(pay_for_damage, (const char *));

src/monmove.c

@@ -1194,6 +1194,9 @@ postmov:
 			(is_pool(mtmp->mx, mtmp->my) && !Is_waterlevel(&u.uz));
 		newsym(mtmp->mx, mtmp->my);
 	    }
+	    if (mtmp->isshk) {
+		after_shk_move(mtmp);
+	    }
 	}
 	return(mmoved);
 }

src/shk.c

@@ -891,6 +891,7 @@ register boolean killkops;
 #endif
 		pacify_guards();
 	}
+	after_shk_move(shkp);
 }
 
 STATIC_OVL boolean
@@ -3257,8 +3258,24 @@ register struct monst *shkp;
 		}
 	}
 
-	return(move_special(shkp,inhishop(shkp),
-			    appr,uondoor,avoid,omx,omy,gx,gy));
+	z = move_special(shkp,inhishop(shkp),appr,uondoor,avoid,omx,omy,gx,gy);
+	if (z > 0) after_shk_move(shkp);
+
+	return z;
+}
+
+/* called after shopkeeper moves, in case the move causes re-entry into shop */
+void
+after_shk_move(shkp)
+struct monst *shkp;
+{
+	struct eshk *eshkp = ESHK(shkp);
+
+	if (eshkp->bill_p == (struct bill_x *) -1000 && inhishop(shkp)) {
+	    /* reset bill_p, need to re-calc player's occupancy too */
+	    eshkp->bill_p = &eshkp->bill[0];
+	    check_special_room(FALSE);
+	}
 }
 
 #endif /*OVL3*/