One error turns all warnings into errors

[birkhola]

Dealing with errors in javadoc generation is difficult due to a logging bug in the plugin. Whenever an error occurs that makes the javadoc command fail lots of issues, that are logged as warnings for usual turn into logging errors, which makes it kind of hard to find out which issues really caused the failure.

[ktoso]

Can't remember if this actually wasn't an issue with javadoc.
PR to help address this would be very welcome