(svn r6047) -Codechange: FOR_ALL now _only_ loops valid items, and skips invalid ones

-Codechange: use IsValidXXX where ever possible
  Note: both changes to prepare for new pool system, which needs those changes.
  For every pool there are 2 ugly lines, which will be removed when done
  implementing new pool system.
  Based on FS#13 by blathijs, partly implemented.

npf.c

@@ -792,7 +792,7 @@ NPFFoundTargetData NPFRouteToDepotTrialError(TileIndex tile, Trackdir trackdir,
 	FOR_ALL_DEPOTS(depot) {
 		/* Check if this is really a valid depot, it is of the needed type and
 		 * owner */
-		if (IsValidDepot(depot) && IsTileDepotType(depot->xy, type) && IsTileOwner(depot->xy, owner))
+		if (IsTileDepotType(depot->xy, type) && IsTileOwner(depot->xy, owner))
 			/* If so, let's add it to the queue, sorted by distance */
 			depots.push(&depots, depot, DistanceManhattan(tile, depot->xy));
 	}