polymorph engulfing monster display bit

- <Someone> reported that the swallowed display did not update immediately if
you managed to polymorph the monster that was engulfing you into another
engulfing monster

doc/fixes34.1

@@ -76,6 +76,8 @@ don't crash when angry shopkeeper re-enters the shop and you pick up something
 monsters with WAITFORU strategy should act if successfully attacked by
 	non-damaging attacks (e.g. seduction, rust damage)
 don't summon kops if credit covers cost of unpaid goods taken out of shop
+update swallowed display immediately if an engulfing monster polymorphs
+	into another engulfing monster
 
 
 Platform- and/or Interface-Specific Fixes

src/mon.c

@@ -2368,6 +2368,9 @@ boolean polyspot;	/* change is the result of wand or spell of polymorph */
 					mtmp->mhp = 1;  /* almost dead */
 				}
 				expels(mtmp, olddata, FALSE);
+			} else {
+				/* update swallow glyphs for new monster */
+				swallowed(0);
 			}
 		} else if (!sticks(mdat) && !sticks(youmonst.data))
 			unstuck(mtmp);