shopkeeper falling thru a hole left unpaid objects unpaid

Reported to the list.  Player breaks a wand of digging causing the
shopkeeper to fall.  This didn't clear unpaid items.  For now, this can
only occur due to player action, so added a call to make_angry_shk to
handle this situation.

src/dig.c

@@ -632,6 +632,7 @@ int ttyp;
 			} else {
 			    get_level(&tolevel, depth(&u.uz) + 1);
 			}
+			if (mtmp->isshk) make_angry_shk(mtmp, 0, 0);
 			migrate_to_level(mtmp, ledger_no(&tolevel),
 					 MIGR_RANDOM, (coord *)0);
 		    }