[client-v2] Fix ClickHouseLZ4OutputStream sending extra bytes when income buffer is empty

[chernser]

Summary

If ClickHouseLZ4OutputStream#flush() is called when input buffer is empty (no data to compress) then ClickHouseLZ4OutputStream will create an empty frame that will cause error on server side like:
Can't decompress data: header is corrupt with decompressed block size 0: While executing ParallelParsingBlockInputFormat. (CANNOT_DECOMPRESS)

Closes: #1993

Checklist

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• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials