improve path_to_filesystem() performance

radicale/pathutils.py

@@ -286,10 +286,9 @@ def path_to_filesystem(root: str, sane_path: str) -> str:
         safe_path = os.path.join(safe_path, part)
         # Check for conflicting files (e.g. case-insensitive file systems
         # or short names on Windows file systems)
-        if os.path.lexists(safe_path):
-            with os.scandir(safe_path_parent) as entries:
-                if part not in (e.name for e in entries):
-                    raise CollidingPathError(part)
+        if (os.path.lexists(safe_path) and
+          not os.path.realpath(safe_path).endswith(part)):
+            raise CollidingPathError(part)
     return safe_path