(svn r18473) -Fix (r18470): crash when moving a multiheaded part to be just after itself

src/train_cmd.cpp

@@ -1368,9 +1368,12 @@ CommandCost CmdMoveRailVehicle(TileIndex tile, DoCommandFlag flags, uint32 p1, u
 
 	if (src->IsRearDualheaded()) return_cmd_error(STR_ERROR_REAR_ENGINE_FOLLOW_FRONT);
 
-	/* when moving all wagons, we can't have the same src_head and dst_head */
+	/* When moving all wagons, we can't have the same src_head and dst_head */
 	if (move_chain && src_head == dst_head) return CommandCost();
 
+	/* When moving a multiheaded part to be place after itself, bail out. */
+	if (!move_chain && dst->IsRearDualheaded() && src == dst->other_multiheaded_part) return CommandCost();
+
 	/* Check if all vehicles in the source train are stopped inside a depot. */
 	if (!src_head->IsStoppedInDepot()) return_cmd_error(STR_ERROR_TRAINS_CAN_ONLY_BE_ALTERED_INSIDE_A_DEPOT);