Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=57284
Enable startAsync() to be called from a Filter and still be able to call
the remainder of the FilterChain

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1643371 13f79535-47bb-0310-9956-ffa450edef68