Changed test for when AllowedPrinciples == null

If there are no restrictions on the allowed users all users should be granted access.
Before none were granted access. Changed comparison to reflect this.
Fix for decodeBase64 only accepting bytes, not String

Base64.decodeBase64 in WebauthDecoder.java was found to only accept bytes as oppose
to Strings. .getBytes() was added to buff.toString() to fix this.
Merge pull request #1 from Jocbe/master

Bugfix for when allowedPrincipals == null