Stopping the server reader can cause an exception when reading.

[ph]

Beats input: unhandled exception {:exception=>#<LogStash::Json::ParserError: Unexpected character ('J' (code 74)): Expected space separating root-level values at [Source: [B@34945110; line: 1, column: 3]>, :backtrace=>["/Users/ph/es/logstash/lib/logstash/json.rb:41:in jruby_load'", "/Users/ph/es/logstash/lib/logstash/json.rb:38:injruby_load'", "/Users/ph/es/ruby-lumberjack/lib/lumberjack/server.rb:246:in json_data_payload'", "/Users/ph/es/ruby-lumberjack/lib/lumberjack/server.rb:163:infeed'", "/Users/ph/es/ruby-lumberjack/lib/lumberjack/server.rb:330:in read_socket'", "/Users/ph/es/ruby-lumberjack/lib/lumberjack/server.rb:315:inrun'", "/Users/ph/es/logstash-plugins/logstash-input-beats/lib/logstash/inputs/beats.rb:149:in invoke'", "org/jruby/RubyProc.java:271:incall'", "/Users/ph/es/logstash/vendor/bundle/jruby/1.9/gems/concurrent-ruby-0.9.1-java/lib/concurrent/executor/executor_service.rb:515:in run'", "Concurrent$$JavaExecutorService$$Job_310320422.gen:13:inrun'"], :level=>:error}