When sending mail notifications, the canonical address format (rig/name)
doesn't distinguish between crew workers (session: gt-rig-crew-name) and
polecats (session: gt-rig-name). This caused notifications to fail for
crew workers in other rigs.
Solution: Try both possible session IDs when the address is ambiguous,
using the first one that has an active session.
Supersedes PR #896 which only handled slash-to-dash conversion.
Fixes: gt-h5btjg
db60489d0f