Whiteout directory not work.

[pigfall]

Reproduce steps:

• Download and prepare the layers fuse-layers.zip

#!/bin/bash
set -e
mkdir -p /tmp/reproduce
cd /tmp/reproduce
curl -LO https://github.com/user-attachments/files/15951378/fuse-layers.zip
unzip fuse-layers.zip
cd fuse-layers
mkdir -p merged
fuse-overlayfs -o lowerdir="$(pwd)/l1:$(pwd)/l0" merged

• Reproduce the bug by access files in following sequence

#!/bin/bash
# Result is as expected.
ls /tmp/reproduce/fuse-layers/merged/site-packages > /dev/null

# Result is as expected.
ls /tmp/reproduce/fuse-layers/merged/site-packages/setuptools > /dev/null

# Result is wrong. Beacuse there is whiteout file in `l1/site-package/setuptools/.wh..wh.opq`, so we should only see the file `depends.cpython-38.pyc` from `l1`.  But result is `config.cpython-38.pyc  depends.cpython-38.pyc` which are from `l0`
ls /tmp/reproduce/fuse-layers/merged/site-packages/setuptools/__pycache__

echo ''
echo 'Result is wrong. Beacuse there is whiteout file in `l1/site-package/setuptools/.wh..wh.opq`, so we should only see the file `depends.cpython-38.pyc` from `l1`.  But result is `config.cpython-38.pyc  depends.cpython-38.pyc` which are from `l0`'