office2john - assertion error in find_table on very old word document

I have found very old Microsoft Word documents protected by pass (old letters). They are from years 1998-2000, so I am expecting Microsoft Office 97 format.

When I try:
python3 office2john.py letter.doc

the result is

Traceback (most recent call last):
  File "/tmp/john-bleeding-jumbo/run/office2john.py", line 3151, in <module>
    ret = process_file(sys.argv[i])
  File "/tmp/john-bleeding-jumbo/run/office2john.py", line 3081, in process_file
    stream = find_table(filename, sdoc)
  File "/tmp/john-bleeding-jumbo/run/office2john.py", line 2461, in find_table
    assert(w_ident == b"\xec\xa5")
AssertionError

Looks like this line https://github.com/openwall/john/blob/342364206fa9bfc129c6ef78fd2770f91e137b74/run/office2john.py#L2461 is asserting some header, but it is not there. Unfortunately, those letters are personal, so I cannot post whole file simply here.

xxd -l 208 letter.doc 
00000000: d0cf 11e0 a1b1 1ae1 0000 0000 0000 0000  ................
00000010: 0000 0000 0000 0000 3e00 0300 feff 0900  ........>.......
00000020: 0600 0000 0000 0000 0000 0000 0100 0000  ................
00000030: 1f00 0000 0000 0000 0010 0000 2000 0000  ............ ...
00000040: 0100 0000 feff ffff 0000 0000 1e00 0000  ................
00000050: ffff ffff ffff ffff ffff ffff ffff ffff  ................
00000060: ffff ffff ffff ffff ffff ffff ffff ffff  ................
00000070: ffff ffff ffff ffff ffff ffff ffff ffff  ................
00000080: ffff ffff ffff ffff ffff ffff ffff ffff  ................
00000090: ffff ffff ffff ffff ffff ffff ffff ffff  ................
000000a0: ffff ffff ffff ffff ffff ffff ffff ffff  ................
000000b0: ffff ffff ffff ffff ffff ffff ffff ffff  ................
000000c0: ffff ffff ffff ffff ffff ffff ffff ffff  ................

I was looking if is something is missing (some library) or if office2john is not supporting so old office files, but no luck.

Start in run/office2john.py at process_file and find_table, especially the assertion around the expected header. Reproduce the failure with an old Microsoft Word document or the supplied initial hex dump, then determine the supported handling for this format. Done means the input no longer triggers an AssertionError and office2john reports an appropriate result.