[appleconnect] fix extractor

[ghost]

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

1. I happened to find that appleconnect extractor fails. I get:

$ youtube-dl https://itunes.apple.com/us/post/idsa.4ab17a39-2720-11e5-96c5-a5b38f6c42d3 --ignore-config -v -F
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'https://itunes.apple.com/us/post/idsa.4ab17a39-2720-11e5-96c5-a5b38f6c42d3', u'--ignore-config', u'-v', u'-F']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2021.05.16
[debug] Python version 2.7.10 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.4, ffprobe 4.4, phantomjs 2.1.1
[debug] Proxy map: {}
[AppleConnect] 4ab17a39-2720-11e5-96c5-a5b38f6c42d3: Downloading webpage
ERROR: Unable to extract like count; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

The like count, or 'n Loves', doesn't exist in the webpage now. Since it is an optional field, and there may be some possibility that it comes back again, I changed the default value None to be returned.

2. While doing above, I found another type of url https://itunes.apple.com/us/post/sa.0fe0229f-2457-11e5-9f40-1bb645f2d5d9. This url can be handled by the generic extractor now, I thought it better to be handled by appleconnect extractor so I changed _VALID_URL to accept it.