Fix: Avoid iteration errors caused by None when reading Nihon Kohden .LOG files

This is a follow-up to #13251. In #13251, some additional checks were added to
`_read_event_log_block` (including a version check), which could cause
`_read_event_log_block` to return `None`, leading to iteration errors.

This change avoids that issue by returning an empty array instead of `None` when
reading fails. In addition, when the version does not match, a warning is now
issued instead of returning `None`.

Author: myd7349

doc/changes/dev/13915.bugfix.rst

@@ -0,0 +1 @@
+Fix iteration errors caused by `_read_event_log_block` returning `None` when reading Nihon Kohden log files, by `Tom Ma`_.

mne/io/nihon/nihon.py

@@ -289,21 +289,23 @@ def _read_nihon_header(fname):
 
 
 def _read_event_log_block(fid, t_block, version):
+    empty_logs = np.empty(0, dtype="|S45")
+
     fid.seek(0x92 + t_block * 20)
     data = np.fromfile(fid, np.uint32, 1)
     if data.size == 0 or data[0] == 0:
-        return
+        return empty_logs
     t_blk_address = data[0]
 
     fid.seek(t_blk_address + 0x1)
     data = np.fromfile(fid, "|S16", 1).astype("U16")
     if data.size == 0 or data[0] != version:
-        return
+        warn(f"Event log version mismatch: expected '{version}', got '{data}'")
 
     fid.seek(t_blk_address + 0x12)
     data = np.fromfile(fid, np.uint8, 1)
     if data.size == 0:
-        return
+        return empty_logs
     n_logs = data[0]
 
     fid.seek(t_blk_address + 0x14)