Merge branch 'hf/unpack-trees-quadratic-scan'

The cache-scanning loop in 'next_cache_entry()' has been optimized to avoid rescanning already-unpacked index entries, preventing a quadratic performance slow-down when diffing the working tree against a commit with a pathspec matching early index entries. * hf/unpack-trees-quadratic-scan: unpack-trees: avoid quadratic index scan in next_cache_entry()