north-south drawbridge

From a bug report:  zapping a wand of striking or locking or spell of
force bolt or wizard lock up or down when standing at an open drawbridge's
portcullis didn't affect the bridge if the portcullis was positioned north
of the open span.  One of the two drawbridges on the Valkyrie quest goal
level has that orientation.  is_drawbridge_wall()'s name is somewhat
misleading; it isn't boolean and returns -1 rather than 0 for "no".

doc/fixes34.4

@@ -277,6 +277,8 @@ wielding a cloak of magic resistance or gray dragon scales, or carrying one in
 	to polymorphed hero
 wielding a potion of blindness or carrying one in alternate weapon or quiver
 	slot conferred resistance against light-based blindness to any hero
+zapping closing or breaking magic up or down from beneath an open drawbridge's
+	portcullis failed if bridge orientation was north-to-south (Valk quest)
 
 
 Platform- and/or Interface-Specific Fixes

src/zap.c

@@ -2495,7 +2495,7 @@ struct obj *obj;	/* wand or spell */
 	case SPE_WIZARD_LOCK:
 	    /* down at open bridge or up or down at open portcullis */
 	    if (((levl[x][y].typ == DRAWBRIDGE_DOWN) ? (u.dz > 0) :
-			(is_drawbridge_wall(x,y) && !is_db_wall(x,y))) &&
+			(is_drawbridge_wall(x,y) >= 0 && !is_db_wall(x,y))) &&
 		    find_drawbridge(&xx, &yy)) {
 		if (!striking)
 		    close_drawbridge(xx, yy);