Ethsigner fails to read empty password files and crashes

[jframe]

Hi,

This looks like a regression somewhere. When I attempt to pass in an empty password file with v 21.3.0 I get the following error:

jfernandes@falcon:~/workspace/quorum-performance/besu(main)$ docker logs 265aae1a50cc
Setting logging level to INFO
2021-05-18 02:13:39.304+00:00 | main | INFO  | SignerSubCommand | Version = ethsigner/v21.3.0/linux-x86_64/-na-openjdk64bitservervm-java-11
2021-05-18 02:13:39.464+00:00 | main | ERROR | PasswordFileUtil | Cannot read password from empty file: /opt/ethsigner/passwordfile
Failed to construct a signer from supplied arguments.
Cause: Cannot read password from empty file: /opt/ethsigner/passwordfile
Usage: ethsigner file-based-signer [-hV] [-k=<FILE>] [-p=<FILE>]
Sign transactions with a key stored in an encrypted V3 Keystore file.
  -h, --help              Show this help message and exit.
  -k, --key-file=<FILE>   The path to a file containing the key used to sign
                            transactions.
  -p, --password-file=<FILE>
                          The path to a file containing the password used to
                            decrypt the keyfile.
  -V, --version           Print version information and exit.

This works fine on v0.6.0 though, which just starts up fine and handles requests

For ref the password file is https://github.com/ConsenSys/quorum-performance/blob/main/besu/config/besu/passwords.txt

To reproduce:

1. Change this line https://github.com/ConsenSys/quorum-performance/blob/main/besu/docker-compose.yml#L318 to 21.3.0
2. Run ./run.sh
3. Check logs, all other ethsigners on 0.6.0 are fine, except this one which would have crashed