[ImageBam] Deleted images throw TypeError

[taskhawk]

Example: https://www.imagebam.com/image/40a481151474621

$ gallery-dl --config-ignore -vK "http://www.imagebam.com/image/40a481151474621"
[gallery-dl][debug] Version 1.31.2
[gallery-dl][debug] Python 3.12.3 - Linux-6.14.0-37-generic-x86_64-with-glibc2.39
[gallery-dl][debug] requests 2.32.3 - urllib3 2.4.0
[gallery-dl][debug] Configuration Files []
[gallery-dl][debug] Starting KeywordJob for 'http://www.imagebam.com/image/40a481151474621'
[imagebam][debug] Using ImagebamImageExtractor for 'http://www.imagebam.com/image/40a481151474621'
[urllib3.connectionpool][debug] Starting new HTTPS connection (1): www.imagebam.com:443
[urllib3.connectionpool][debug] https://www.imagebam.com:443 "GET /image/40a481151474621 HTTP/1.1" 200 None
[imagebam][error] An unexpected error occurred: TypeError - argument of type 'NoneType' is not iterable. Please run gallery-dl again with the --verbose flag, copy its output and report this issue on https://github.com/mikf/gallery-dl/issues .
[imagebam][debug] 
Traceback (most recent call last):
  File "/home/user/.gallery-dl/lib/python3.12/site-packages/gallery_dl/job.py", line 158, in run
    msg = self.dispatch(extractor)
          ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.gallery-dl/lib/python3.12/site-packages/gallery_dl/job.py", line 209, in dispatch
    for msg, url, kwdict in messages:
  File "/home/user/.gallery-dl/lib/python3.12/site-packages/gallery_dl/extractor/imagebam.py", line 96, in items
    image = self._parse_image_page(path)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.gallery-dl/lib/python3.12/site-packages/gallery_dl/extractor/imagebam.py", line 31, in _parse_image_page
    filename = text.unescape(text.extract(page, 'alt="', '"', pos)[0])
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/html/__init__.py", line 130, in unescape
    if '&' not in s:
       ^^^^^^^^^^^^
TypeError: argument of type 'NoneType' is not iterable