Don't fail if faucet chain was opened but old one not closed.

[afck]

Motivation

On the testnet, for some reason the faucet failed to close the old chain after migrating to a new one.

Proposal

Make the faucet handle that case on startup: Also migrate if the old chain has no tokens, even if it is not closed.

Test Plan

A new test for all these cases was added.

Release Plan

• These changes should be ported to the main branch.
• We should try this on the faucet with the a3edc33d8e951a1139333be8a4b56646b5598a8f51216e86592d881808972b07 chain.

Links

• Extending the functionality from #3863.
• reviewer checklist