ValueError: Parsing attachment number from appellate attachment page

[sentry]

Sentry Issue: COURTLISTENER-AR1

The attachment number parsing is failing in this appellate attachment page:

ca5_00507653414.txt

ValueError: invalid literal for int() with base 10: ''
(2 additional frame(s) were not displayed)
...
  File "cl/recap/tasks.py", line 2211, in fetch_attachment_page
    att_data = att_data_parser(text, court_id)
  File "cl/recap/mergers.py", line 1527, in get_data_from_appellate_att_report
    att_data = att_page.data

Filed by: @albertisfu