Proposed fix for  LOGSTASH-884 and LOGSTASH-1060

I've made this small modification to the Gelf input (against v1.1.12). I'm running it in production now to see if my problem goes away.
I tried it in my dev environment (using the unpatched jar) sending very large gziped data which would kill the gelf listener, followed by smaller data which go nowhere since the gelf listener was dead.
I then tried it in my dev environment (using the patched jar) sending very large gzipped data which would thrown a parse exception, followed by smaller data which would continue the path through the input -> parse -> output