Logstash crushed when server run out of disk space

One of our servers with Logstash run out of disk space.
This led to crushing of Logstash process with NullPointerException in logs
[logstash.err.txt](https://github.com/elastic/logstash/files/1379977/logstash.err.txt)

- Version: 5.5.2
- Operating System: RHEL7
- Steps to Reproduce:
You need to load a disk with running Logstash with any kind of data until you see a fatal message in logstash-plain log file:
`[FATAL][logstash.runner ] An unexpected error occurred! {:error=>#, :backtrace=>["org/jruby/ext/zlib/JZlibRubyGzipWriter.java:360:in `flush'", "/data/elog/logstash/vendor/bundle/jruby/1.9/gems/logstash-output-file-4.1.0/lib/logstash/outputs/file.rb:293:in `flush'", "/data/elog/logstash/vendor/bundle/jruby/1.9/gems/logstash-output-file-4.1.0/lib/logstash/outputs/file.rb:127:in `multi_receive_encoded'", "org/jruby/RubyHash.java:1342:in `each'", "/data/elog/logstash/vendor/bundle/jruby/1.9/gems/logstash-output-file-4.1.0/lib/logstash/outputs/file.rb:124:in `multi_receive_encoded'", "org/jruby/ext/thread/Mutex.java:149:in `synchronize'", "/data/elog/logstash/vendor/bundle/jruby/1.9/gems/logstash-output-file-4.1.0/lib/logstash/outputs/file.rb:123:in `multi_receive_encoded'", "/data/elog/logstash/logstash-core/lib/logstash/outputs/base.rb:90:in `multi_receive'", "/data/elog/logstash/logstash-core/lib/logstash/output_delegator_strategies/shared.rb:13:in `multi_receive'", "/data/elog/logstash/logstash-core/lib/logstash/output_delegator.rb:47:in `multi_receive'", "/data/elog/logstash/logstash-core/lib/logstash/pipeline.rb:420:in `output_batch'", "org/jruby/RubyHash.java:1342:in `each'", "/data/elog/logstash/logstash-core/lib/logstash/pipeline.rb:419:in `output_batch'", "/data/elog/logstash/logstash-core/lib/logstash/pipeline.rb:365:in `worker_loop'", "/data/elog/logstash/logstash-core/lib/logstash/pipeline.rb:330:in `start_workers'"]}`