fix #H2589 - theft vs donning/doffing (trunk only)

From a bug report, having some
armor stolen while in the midst of putting on armor--when both items have
a multiple turn completion delay--could result in side-effects for the
latter item being reversed even though they hadn't been applied yet.  So
you'd lose points of Int and Wis when attempting to put on a positively
enchanted helm of brilliance, or gain such with a negatively enchanted one.

     steal() was assigning to afternmv before it had been used to finish the
action of putting on or taking off armor.  Fix by interrupting the attempt
to put on or take off armor when being victimized by theft (or being hit by
succubus or incubus seduction).  The existing stop_occupation() call wasn't
sufficient because afternmv is different from occupation.

src/do_wear.c

@@ -1203,6 +1203,46 @@ cancel_don()
 	context.takeoff.what = 0L;
 }
 
+/* called by steal() during theft from hero; interrupt donning/doffing */
+int
+stop_donning(stolenobj)
+struct obj *stolenobj;	/* no message if stolenobj is already being doffing */
+{
+    char buf[BUFSZ];
+    struct obj *otmp;
+    boolean putting_on;
+    int result;
+
+    for (otmp = invent; otmp; otmp = otmp->nobj)
+	if ((otmp->owornmask & W_ARMOR) && donning(otmp)) break;
+	/* at most one item will pass donning() test at any given time */
+    if (!otmp) return 0;
+
+    result = -multi;	/* remember this before calling unmul() */
+    /* donning() returns True when doffing too */
+    putting_on = !(context.takeoff.mask & otmp->owornmask);
+    /* cancel_don() looks at afternmv; it also serves as cancel_doff() */
+    cancel_don();
+    /* don't want <armor>_on() or <armor>_off() being called
+       by unmul() since the on or off action isn't completing */
+    afternmv = 0;
+    if (putting_on || otmp != stolenobj)
+	Sprintf(buf, "You stop %s %s.",
+		putting_on ? "putting on" : "taking off",
+		thesimpleoname(otmp));
+    else
+	buf[0] = '\0';	/* silently stop doffing stolenobj */
+    unmul(buf);
+    /* while putting on, item becomes worn immediately but side-effects are
+       deferred until the delay expires; when interrupted, make it unworn
+       (while taking off, item stays worn until the delay expires; when
+       interrupted, leave it worn) */
+    if (putting_on)
+	remove_worn_item(otmp, FALSE);
+
+    return result;
+}
+
 static NEARDATA const char clothes[] = {ARMOR_CLASS, 0};
 static NEARDATA const char accessories[] = {RING_CLASS, AMULET_CLASS, TOOL_CLASS, FOOD_CLASS, 0};