… set

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Instead of suppressing errors with @, check if the path is within
open_basedir restrictions before calling is_readable(). This approach
avoids hiding other potential errors while still preventing warnings
when traversing directories outside allowed paths.

Add is_path_within_open_basedir() helper function that:
- Returns true if no open_basedir restriction is set
- Checks if path starts with any allowed path from open_basedir
- Uses string comparison to avoid triggering warnings on restricted paths

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

- Normalize input directory with realpath() early in find_file_upward()
  to handle relative paths and symlinks properly
- Add safety check for getcwd() returning false
- Update documentation to clarify that is_path_within_open_basedir()
  expects absolute paths
- This addresses security concerns about asymmetric path comparison

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

On Windows, filesystem paths are case-insensitive, so the path comparison
in is_path_within_open_basedir() needs to handle this. Added case-insensitive
comparison using strcasecmp() and stripos() when running on Windows systems
(detected by checking if DIRECTORY_SEPARATOR is backslash).

This ensures that open_basedir checks work correctly on Windows even when
the case of paths doesn't match between open_basedir settings and actual paths.

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>