fix #H6955 - wielded potion 'object lost' panic

Report classified this as 'segfault' but it's actually a controlled
panic().  When hero has lycanthropy and is wielding a potion of unholy
water while in human form, if that potion is boiled then it triggers
a transformation to beast form which in turn causes wielded weapon to
be dropped.  When the code unwinds back up through potionbreathe() to
destroy_item(), the boiled potion won't be found in inventory any more
and useup() -> useupall() -> freeinv() -> extract_nobj() panics.

doc/fixes36.1

@@ -521,6 +521,9 @@ prayer boon of 'fix all troubles' could get stuck in an infinite loop for
 	TROUBLE_STUCK_IN_WALL if there was no spot to teleport into available
 It shouldn't be considered hypocrisy if you speed up your pet while standing 
 	on Elbereth
+fix 'object lost' panic if hero with lycanthropy but in human form is wielding
+	a potion of unholy water which gets boiled/exploded by fire, causing
+	were-transformation and drop of wielded weapon
 
 
 Fixes to Post-3.6.0 Problems that Were Exposed Via git Repository

src/polyself.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	polyself.c	$NHDT-Date: 1513298347 2017/12/15 00:39:07 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.116 $ */
+/* NetHack 3.6	polyself.c	$NHDT-Date: 1520797126 2018/03/11 19:38:46 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.117 $ */
 /*      Copyright (C) 1987, 1988, 1989 by Ken Arromdee */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -964,7 +964,7 @@ int alone;
 {
     struct obj *otmp;
     const char *what, *which, *whichtoo;
-    boolean candropwep, candropswapwep;
+    boolean candropwep, candropswapwep, updateinv = TRUE;
 
     if (uwep) {
         /* !alone check below is currently superfluous but in the
@@ -989,17 +989,26 @@ int alone;
                 You("find you must %s %s %s!", what,
                     the_your[!!strncmp(which, "corpse", 6)], which);
             }
+            /* if either uwep or wielded uswapwep is flagged as 'in_use'
+               then don't drop it or explicitly update inventory; leave
+               those actions to caller (or caller's caller, &c) */
             if (u.twoweap) {
                 otmp = uswapwep;
                 uswapwepgone();
-                if (candropswapwep)
+                if (otmp->in_use)
+                    updateinv = FALSE;
+                else if (candropswapwep)
                     dropx(otmp);
             }
             otmp = uwep;
             uwepgone();
-            if (candropwep)
+            if (otmp->in_use)
+                updateinv = FALSE;
+            else if (candropwep)
                 dropx(otmp);
-            update_inventory();
+
+            if (updateinv)
+                update_inventory();
         } else if (!could_twoweap(youmonst.data)) {
             untwoweapon();
         }

src/potion.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	potion.c	$NHDT-Date: 1502753790 2017/08/14 23:36:30 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.138 $ */
+/* NetHack 3.6	potion.c	$NHDT-Date: 1520797133 2018/03/11 19:38:53 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.144 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -1563,6 +1563,11 @@ register struct obj *obj;
     int i, ii, isdone, kn = 0;
     boolean cureblind = FALSE;
 
+    /* potion of unholy water might be wielded; prevent
+       you_were() -> drop_weapon() from dropping it so that it
+       remains in inventory where our caller expects it to be */
+    obj->in_use = 1;
+
     switch (obj->otyp) {
     case POT_RESTORE_ABILITY:
     case POT_GAIN_ABILITY:
@@ -1714,7 +1719,7 @@ register struct obj *obj;
         break;
      */
     }
-    /* note: no obfree() */
+    /* note: no obfree() -- that's our caller's responsibility */
     if (obj->dknown) {
         if (kn)
             makeknown(obj->otyp);