fix: use msg.path instead of nonexistent msg.relpath in fsreport

FileEntry namedtuple has (path, mtime, size), not relpath.
Crashes with AttributeError when --mdir flag is used.

chatmaild/src/chatmaild/fsreport.py

@@ -68,7 +68,7 @@ class Report:
             for size in self.message_buckets:
                 for msg in mailbox.messages:
                     if msg.size >= size:
-                        if self.mdir and not msg.relpath.startswith(self.mdir):
+                        if self.mdir and f"/{self.mdir}/" not in msg.path:
                             continue
                         self.message_buckets[size] += msg.size