Version of EOSJS
All versions

Describe the bug
generateTapos throws an error on transaction when calling get_block_header_state, but does not actually need to call it.

To Reproduce
Steps to reproduce the behavior:

1. Spin up a new chain
2. Generate a transaction
3. Error in console when transact calls generateTapos

Expected behavior
Should not throw if calling generateTapos without a valid last_irreversible_block_num.

Additional context
Porting this over from #698
Co-Authored By: @UMU618 umu618@hotmail.com