[youtube] Ignore invalid stretch ratio

[someziggyman]

Checklist

• I'm reporting a broken site support
• I've verified that I'm running youtube-dl version 2021.04.07
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar issues including closed ones

Verbose log

youtube-dl -v -F https://www.youtube.com/watch?v=FRhJzUSJbGI
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'-F', u'https://www.youtube.com/watch?v=FRhJzUSJbGI']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2021.04.07
[debug] Python version 2.7.16 (CPython) - Darwin-20.3.0-x86_64-i386-64bit
[debug] exe versions: none
[debug] Proxy map: {}
[youtube] FRhJzUSJbGI: Downloading webpage
[youtube] FRhJzUSJbGI: Downloading MPD manifest
Traceback (most recent call last):
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/usr/local/bin/youtube-dl/__main__.py", line 19, in <module>
  File "/usr/local/bin/youtube-dl/youtube_dl/__init__.py", line 475, in main
  File "/usr/local/bin/youtube-dl/youtube_dl/__init__.py", line 465, in _real_main
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 2060, in download
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 799, in extract_info
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 806, in wrapper
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 827, in __extract_info
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 534, in extract
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/youtube.py", line 1710, in _real_extract
ValueError: invalid literal for int() with base 10: ''

Description

Test link:
https://www.youtube.com/watch?v=FRhJzUSJbGI

Tested this fix and it seems to work fine - yt-dlp/yt-dlp@46fff71