[aenetworks] Prevent missing ratings extractor crash

[agibson-fl]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Certain shows without ratings on AE networks will crash and not allow the download to complete.
To duplicate this:
yt-dlp -V https://play.history.com/shows/kennedy/season-1/episode-2
or
yt-dlp -V https://play.history.com/shows/kennedy/season-1/episode-3
(not sure if one will get ratings in the meantime of this being merged and prevent duplication)

I found code already in this project from the amcnetworks.py extractor that fixes the problem there. I copied that code over to the aenetworks.py and tested it manually. It works.

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
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What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[agibson-fl]

@bashonly I pushed the requested changes. The code no longer looks like the convention used in amcnetworks.py, but your suggested changes are cleaner anyway. (I was trying to fit the code in with the other extractors that had this problem)