s3:winbind:pwent: move resetting next_user up.

s3:winbind:pwent: move resetting next_user up.

This does not change the behaviour and makes it more evident
that we have anothe code duplication here:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
if (state->gstate->num_users == 0) {
	...
}

subreq = wb_fill_pwent_send(...)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

is for the current setting of variables equivalent
to the block found elsewhere:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
if (state->gstate->next_user >= state->gstate->num_users) {
	...
}

subreq = wb_fill_pwent_send(...)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

because both num_users is set to a non-negative
value and num_users starts at 0 and is incremented up to
num_users.

The code duplication will be factored out next.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>