HTTP/2 Sonar Bugs

Motivation:
Clinker provides a Sonar tool which detects potential bugs or problems in the code.  These problems were reported here http://clinker.netty.io/sonar/drilldown/issues/io.netty:netty-parent:master?

Modifications:
Make the recommended changes as reported by Sonar

Result:
Better or more standard code.  Less Sonar problem reports for HTTP/2 codec.