drain life vs drain resisting objects (trunk only)

From the newsgroup:  casting spell of drain life at Stormbringer
(or Excalibur or Staff of Aesculapius) would reduce its enchantment just
like any other weapon.  Drain resistance should protect against that even
when not actively wielded.

src/zap.c

@@ -1007,7 +1007,8 @@ register struct obj *obj;
 			obj->oclass != ARMOR_CLASS && !is_weptool(obj)) ||
 			obj->spe <= 0)
 	    return (FALSE);
-	if (obj_resists(obj, 10, 90))
+	if (defends(AD_DRLI, obj) || defends_when_carried(AD_DRLI, obj) ||
+	        obj_resists(obj, 10, 90))
 	    return (FALSE);
 
 	/* Charge for the cost of the object */