linesUtf8 drops a partially buffered line when an empty ByteChunk arrives

[Mendrejk]

Problem

In LinesImpl, an empty ByteChunk currently clears the accumulated line buffer. Mid-record empty chunks therefore silently discard already-seen bytes.

Example

Chunks "12", empty, "3\n" can lose the "12" prefix.

Expected

Empty chunks should be no-ops for framing state.

Suggested tests

• Empty chunk between two parts of one line.
• Empty chunk before a final unterminated record.