fix: broken symlinks with empty targets treated as directories

[veeceey]

Fixes #1715

Problem

When a symlink has an empty target (e.g. created via ln -s "" name), using --group-directories-first would incorrectly sort it alongside real directories. The broken symlink appeared at the top of the listing grouped with directories rather than with regular files.

Root Cause

In link_target(), after read_link returns an empty path, reorient_target_path joins it with the parent directory — which resolves to the parent directory itself. Then std::fs::metadata succeeds on that directory, so points_to_directory() returns true for what is actually a broken symlink.

Fix

Added an early return in link_target() that checks if the path from read_link is empty. If so, the symlink is immediately treated as broken (FileTarget::Broken) before any path resolution happens.

Testing

• Added unit tests for both empty-target symlinks and deleted-target symlinks
• Manually verified with a test directory containing broken symlinks:

# Before fix:
$ eza -1 -l --group-directories-first
drwxr-xr-x  - vc 13 Feb 00:52 src
lrwxr-xr-x  - vc 13 Feb 00:54 empty-target.yml ->     # <-- incorrectly grouped with dirs
.rw-r--r--  0 vc 13 Feb 00:52 file.rs
...

# After fix:
$ eza -1 -l --group-directories-first
drwxr-xr-x  - vc 13 Feb 00:52 src
lrwxr-xr-x  - vc 13 Feb 00:52 dir-symlink -> temp_dir
lrwxr-xr-x  - vc 13 Feb 00:54 empty-target.yml ->     # <-- correctly sorted as non-directory
.rw-r--r--  0 vc 13 Feb 00:52 file.rs
...

All existing tests pass (cargo test — 335 unit tests + integration + doc tests).

[veeceey]

still tracking this — open to any suggestions or changes needed