[slopgobblercobbler]

Fixes #478.

When calling read on an Entry with an empty buffer (&mut []), EntryFields::read matches Some(Ok(0)) from the underlying EntryIo and removes self.data[0], treating zero bytes read as EOF. This discards unread member bytes for subsequent reads.

Per std::io::Read, reading into a zero-length slice should return Ok(0) immediately without advancing or consuming data. Returning Ok(0) when into.is_empty() keeps the current EntryIo entry intact.

Testing

Added empty_buffer_read_does_not_discard_data in tests/all.rs:

cargo test --test all empty_buffer_read_does_not_discard_data
cargo test --test all

All 74 tests in tests/all.rs pass.