Fix: Handle protocal parameters fetch error

[dmurawsky]

We were getting this error when the parameter fetch failed:

 ⨯ TypeError: Cannot convert undefined to a BigInt

This is the error that the fetch was returning.

{
  error: 'Forbidden',
  message: 'Network token mismatch. Are you using token for the correct network? See https://blockfrost.dev/docs/start-building#available-networks',
  status_code: 403
}

This code will surface this error to the user when they forget to update their .env file ;)