fix #H2010 - quaffing wielded potion of polymorph

From a bug report, drinking a potion of
polymorph which is wielded would trigger an "object lost" panic if hero
took on a form that was forced to drop its weapon.  Once weapon/potion
got dropped, subsequent useup() of the potion was no longer operating on
an inventory object.

     Unwield the potion at start of drinking, so that dropping doesn't
come into play.  (If we ever introduce a monster form incapable of
holding inventory so drops everything, this will have to be revisited.)

doc/fixes34.4

@@ -384,6 +384,8 @@ hero poly'd into mimic and hiding as an object via #monster didn't unhide
 	when polymorphing into non-mimic
 message "You hit the  with all your might." could be issued if a boulder
 	went away while it was being dug/broken with a pick-axe
+prevent "object lost" panic if/when drinking a wielded potion of polymorph
+	causes hero's new form to drop weapon
 
 
 Platform- and/or Interface-Specific Fixes

src/potion.c

@@ -1,5 +1,4 @@
 /* NetHack 3.5	potion.c	$Date$  $Revision$ */
-/*	SCCS Id: @(#)potion.c	3.5	2009/01/22	*/
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -423,6 +422,21 @@ dodrink()
 
 	otmp = getobj(beverages, "drink");
 	if(!otmp) return(0);
+
+	/* quan > 1 used to be left to useup(), but we need to force
+	   the current potion to be unworn, and don't want to do
+	   that for the entire stack when starting with more than 1.
+	   [Drinking a wielded potion of polymorph can trigger a shape
+	   change which causes hero's weapon to be dropped.  In 3.4.x,
+	   that led to an "object lost" panic since subsequent useup()
+	   was no longer dealing with an inventory item.  Unwearing
+	   the current potion is intended to keep it in inventory.] */
+	if (otmp->quan > 1L) {
+	    otmp = splitobj(otmp, 1L);
+	    otmp->owornmask = 0L;	/* rest of original stuck unaffected */
+	} else if (otmp->owornmask) {
+	    remove_worn_item(otmp, FALSE);
+	}
 	otmp->in_use = TRUE;		/* you've opened the stopper */
 
 	potion_descr = OBJ_DESCR(objects[otmp->otyp]);