jail: Fix regression panic from eb8dcdeac22d

And possibly infinite loop calling prison_ip_restrict() in
kern_jail_set() [2].

[1] It is possible that prisons do not have any IPv4 or IPv6 addresses.
[2] If prison_ip_restrict() is not provided with prison_ip, when it

allocates prison_ip successfully, then it should return false to
indicate not redo prison_ip_restrict() later.

Reviewed by: glebius
Approved by: kp (mentor)
Fixes: eb8dcdeac22d jail: network epoch protection for IP address lists
Differential Revision: https://reviews.freebsd.org/D37906