Replace 'null input buffer' message from Cipher.doFinal() with more i…

[csutherl]

…nformative message by catching empty vault data before passing to Cipher, logging it, and throwing an exception.

With this commit we see the following:

SEVERE: Data not found in alias (my_vault) for VAULT::my_block::manager_password1::
org.apache.tomcat.vault.security.vault.SecurityVaultException: Data not found in alias (my_vault) for VAULT::my_block::manager_password1::
	at org.apache.tomcat.vault.security.vault.PicketBoxSecurityVault.retrieve(PicketBoxSecurityVault.java:272)
....

instead of:

SEVERE [main] org.apache.tomcat.vault.util.PropertySourceVault.getProperty java.lang.IllegalArgumentException: Null input buffer
--
org.apache.tomcat.vault.security.vault.SecurityVaultException: java.lang.IllegalArgumentException: Null input buffer
at org.apache.tomcat.vault.security.vault.PicketBoxSecurityVault.retrieve(PicketBoxSecurityVault.java:299)
....