ListHDFS fails when HDFS URI in Directory property does not contain the host:port part

The scheme and authority (host:port) part of the HDFS URI comes from the core-site.xml but it is also possible to specify a full HDFS URI (e.g. hdfs://myhost:9000/path/to/dir) in the Directory property in ListHDFS (instead of simply /path/to/dir).

NIFI-8737 introduced a warning message when the HDFS URI specified in the Directory property does not match the URI in core-site.xml. However, this validation logic does not handle URIs having a scheme but no authority part properly and results in NPE.