Tidy up the directory reading

doc/changes/devel/13268.bugfix.rst

@@ -0,0 +1 @@
+Fixed bug where the file_id is not set when the file contains a directory at the end of the file, by `Théodore Papadopoulo`_.

mne/_fiff/tag.py

@@ -363,7 +363,7 @@ def _read_dir_entry_struct(fid, tag, shape, rlims):
     """Read dir entry struct tag."""
     pos = tag.pos + 16
     entries = list()
-    for offset in range(1, tag.size // 16):
+    for offset in range(tag.size // 16):
         ent = _read_tag_header(fid, pos + offset * 16)
         # The position of the real tag on disk is stored in the "next" entry within the
         # directory, so we need to overwrite ent.pos. For safety let's also overwrite