Function read_varint_word_tail 

fn read_varint_word_tail(data: &[u8], len: usize) -> u64

The payload of a variable-length integer whose datum ends within eight bytes of the end of data, so the wide load in read_varint_word would run off the end.

Out of line and cold: this is at most the tail of a row, or of a nested list or map.