fixes getUnspentNotes when confirmations >= chain length

[hughy]

Summary

if the length of the chain is shorter than or equal to the confirmation range then we calculate a non-positive number for the maximum confirmed sequence. this results in an error when attempting to construct a key range for loading unspent notes from the unspentNoteHashes index.

the genesis block is always confirmed, so the maximum confirmed sequence can never be less than 1.

fixes getUnspentNotes by setting maxConfirmedSequence to be at least 1.

Testing Plan

• added unit test
• steps to reproduce error:

> yarn start start -d ~/.ironfish-1
> yarn start wallet:import -d ~/.ironfish-1
> yarn start wallet:rescan --reset -d ~/.ironfish-1
> yarn start wallet:send --rawTransaction --offline --datadir=~/.ironfish-1 -t 0e0e42628ae521b5971b6a6c0384e41a623e6332249f86ef080184440d5e0840 -a 1 -o 0.00000001

receive error The value of "value" is out of range. It must be >= 0 and <= 4294967295. Received -1 before applying chanes

Documentation

Does this change require any updates to the Iron Fish Docs (ex. the RPC API
Reference)? If yes, link a
related documentation pull request for the website.

[ ] Yes

Breaking Change

Is this a breaking change? If yes, add notes below on why this is breaking and
what additional work is required, if any.

[ ] Yes