Fixed unintentionally finished of the page output after the first file was processed.

[t3t5u]

Problem Overview

When the input is multiple files, the second and subsequent files are not output.

Cause of the Problem

Calling the PageBuilder#finish will invoke the PageOutput#finish.

https://github.com/embulk/embulk/blob/v0.11.4/embulk-core/src/main/java/org/embulk/spi/PageBuilderImpl.java#L255-L258

    public void finish() {
        doFlush();
        output.finish();
    }

Once the PageOutput#finish is invoked, the outputWorkers will be done and PageOutput#add will no longer work.

https://github.com/embulk/embulk/blob/v0.11.4/embulk-core/src/main/java/org/embulk/exec/LocalExecutorPlugin.java#L456-L463

        public void finish() {
            completeWorkers();
            for (int i = 0; i < scatterCount; i++) {
                if (filtereds[i] != null) {
                    filtereds[i].finish();
                }
            }
        }

https://github.com/embulk/embulk/blob/v0.11.4/embulk-core/src/main/java/org/embulk/exec/LocalExecutorPlugin.java#L444-L454

        public void add(Page page) {
            OutputWorker worker = outputWorkers[(int) (pageCount % scatterCount)];
            if (worker != null) {
                try {
                    worker.add(page);
                } catch (InterruptedException ex) {
                    throw new RuntimeException(ex);
                }
            }
            pageCount++;
        }

Therefore, the second and subsequent files will not be output.

[t3t5u]

@hishidama
Please review. 🙇