BUG: Fix filter_func logging for config.debug=true

[original-brownbear]

Fixes this error reported by @ruflin :

logstash_1       | [2017-10-09T11:57:22,917][ERROR][logstash.pipeline        ] Exception in pipelineworker, the pipeline stopped processing new events, please check your filter configuration and restart Logstash. {:pipeline_id=>"main", "exception"=>"undefined method `to_hash' for [#<LogStash::Event:0x2122ce71>]:Array\nDid you mean?  to_h", "backtrace"=>["(eval):22:in `block in filter_func'", "/opt/logstash-7.0.0-alpha1-SNAPSHOT/logstash-core/lib/logstash/pipeline.rb:499:in `filter_batch'", "/opt/logstash-7.0.0-alpha1-SNAPSHOT/logstash-core/lib/logstash/pipeline.rb:478:in `worker_loop'", "/opt/logstash-7.0.0-alpha1-SNAPSHOT/logstash-core/lib/logstash/pipeline.rb:437:in `block in start_workers'"], :thread=>"#<Thread:0x6d57e27d sleep>"}

that resulted from events now being an [] for filter here as a result of #8428.

I know this isn't 100% perfect since we're now not logging each event before it hits the filter itself, but rather logging the whole batch before running the filter on it.
But the multi_filter method on FilterDelegator simply is what it is and works on batches instead of single events.

[jsvd]

LGTM, tested and confirmed patch makes the test pass

[original-brownbear]

@jsvd thanks merging :)

[elasticsearch-bot]

Armin Braun merged this into the following branches!

Branch	Commits
master	b5062e7
6.x	acad8ba

[elasticsearch-bot]

Armin Braun merged this into the following branches!

Branch	Commits
6.0	550a6ea