[SPARK-16432] Empty blocks fail to serialize due to assert in ChunkedByteBuffer

## What changes were proposed in this pull request?

It's possible to also change the callers to not pass in empty chunks, but it seems cleaner to just allow `ChunkedByteBuffer` to handle empty arrays. cc JoshRosen

## How was this patch tested?

Unit tests, also checked that the original reproduction case in https://github.com/apache/spark/pull/11748#issuecomment-230760283 is resolved.

Author: Eric Liang <ekl@databricks.com>

Closes #14099 from ericl/spark-16432.