command_process_create_cell: calls channel_send_destroy() for already exist circuit

command_process_create_cell tries to check several conditions and can to call channel_send_destroy for already exist circuit. channel_send_destroy is more complex mechanism than sending of some cell as it happened before. It shouldn't to call channel_send_destroy if circ_id already exist for chan. It should to check circ_id and drop if already exist and only then to check all another stuff.