Removed unreachable condition and fixed exception message in transaction.get_multisig_script.
Removed unreachable condition and fixed exception message in transaction.get_multisig_script.

CounterpartyXCP/counterparty-lib,F483/counterparty-lib,monaparty/counterparty-lib,CounterpartyXCP/counterparty-lib,monaparty/counterparty-lib,jarymoth/counterpartyd,coinwarp/dogeparty-lib,tokenly/counterparty-lib,stefcrypto/counterparty-lib,F483/counterparty-lib