mod_http2: adding defensive code for stream EOS handling, in case the request handler

     missed to signal it the normal way (eos buckets). Addresses github issues 
     https://github.com/icing/mod_h2/issues/164, https://github.com/icing/mod_h2/issues/167
     and https://github.com/icing/mod_h2/issues/170. 



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1843426 13f79535-47bb-0310-9956-ffa450edef68