fix(extractor): do not use Path.readlink to check for empty targets

We cannot use Path.readlink to check if the symlink target is
not set (that happens with f_badsymlinks.img on Darwin systems, you need
a broken filesystem and an OS that supports it).

That's because Path.readlink returns a Path object with an empty name
(i.e. Path("")), which is indiscernable from a symlink target that is
the current directory (i.e. Path(".")). Since there is no difference
between Path("") and Path("."), we can't differentiate between a symlink
with an empty target and a symlink that points at the current directory.

unblob/extractor.py

@@ -65,12 +65,13 @@ def fix_symlink(path: Path, outdir: Path, task_result: TaskResult) -> Path:
         path.unlink()
         return path
 
-    target = path.readlink()
-    if not target.name:
+    raw_target = os.readlink(path)  # noqa: PTH115
+    if not raw_target:
         logger.error("Symlink with empty target, removing.")
         path.unlink()
         return path
 
+    target = Path(raw_target)
     if target.is_absolute():
         target = Path(target.as_posix().lstrip("/"))
     else: