Equivalent transformation:
	Handling of bogus requests taken into do_pd_io_start() - we
	call next_request(0) as we would for any other error.  We
	need to call pi_unclaim() before that - on other paths that
	would happen as a side effect of pi_disconnect().
	Setting variables moved into do_pd_io_start() - they don't
	need pd_lock being held, so we can shift that outside.