[ecash-herald] Handle error if getTokenInfoMap is provided with a non-tokenId txid

Summary:
T2972

This console.assert ended up throwing an error if the result is such that txDetails.slpTxData is undefined.

Refactor to catch error if unable to get genesisInfo.

Test Plan:
npm test
npm run sendMsgByBlock 798428 and msg sends, expected error msg is logged

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14160