Invalid --dateafter crashes with no useful error

[TorC8]

• [x ] I've verified and I assure that I'm running youtube-dl 2018.11.07
• [x ] At least skimmed through the README, most notably the FAQ and BUGS sections
• [ x] Searched the bugtracker for similar issues including closed ones

What is the purpose of your issue?

• [x ] Bug report (encountered problems with youtube-dl)

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Description:

With a typo in the --dateafter making a nine digit number (in the below example, an extra 1 in the month), youtube-dl crashes without a useful error message for debugging the command. (Edited for clarity)

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Minimal example command:

$ youtube-dl -v --dateafter 201811106
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'--dateafter', u'201811106']
Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/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 472, in main
  File "/usr/local/bin/youtube-dl/youtube_dl/__init__.py", line 220, in _real_main
  File "/usr/local/bin/youtube-dl/youtube_dl/utils.py", line 1330, in __init__
  File "/usr/local/bin/youtube-dl/youtube_dl/utils.py", line 1311, in date_from_str
  File "/usr/lib/python2.7/_strptime.py", line 335, in _strptime
    data_string[found.end():])
ValueError: unconverted data remains: 6

$ youtube-dl --version
2018.11.07

[TorC8]

Ran a couple extra tests. Looks like a short date either works, but may act on a wrong date, or throws a ValueError complaining about an invalid date format. Given what module throws the error, depending on how youtube-dl is allowed to handle errors, this may be an upstream bug.

Fix is probably to add a corrected version of the following to date_from_str in youtube-dl/utils at around line 1811:

if date_str in == re.match(r'^\d{7..}$', date_str)
    report_invalid_date_and_quit