BUNNYDNS: Permit SRV "." targets

[tlimoncelli]

Fixes #3997

Issue

BunnyDNS no longer prohibits SRV "null targets".

Resolution

Permit them.

[pro-sumer]

Verified that this works:

CONCURRENTLY checking for 0 zone(s)
SERIALLY checking for 1 zone(s)
Serially checking for zone: "example.com"
CONCURRENTLY gathering records of 0 zone(s)
SERIALLY gathering records of 1 zone(s)
Serially Gathering: "example.com"
******************** Domain: example.com
1 correction (bunny_dns)
#1: + CREATE __submission._tcp.example.com SRV 0 0 0 . ttl=86400
SUCCESS!
Done. 1 corrections.

(also checked the Bunny dashboard to confirm)

🎉