Video name start with "."

[SuWeiBo]

Please follow the guide below

• You will be asked some questions and requested to provide some information, please read them carefully and answer honestly
• Put an x into all the boxes [ ] relevant to your issue (like this: [x])
• Use the Preview tab to see what your issue will actually look like

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Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2019.01.24. If it's not, read this FAQ entry and update. Issues with outdated version will be rejected.

• I've verified and I assure that I'm running youtube-dl 2019.01.24

Before submitting an issue make sure you have:

• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

What is the purpose of your issue?

• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
• Question
• Other

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If the purpose of this issue is a bug report, site support request or you are not completely sure provide the full verbose output as follows:

Add the -v flag to your command line you run youtube-dl with (youtube-dl -v <your command line>), copy the whole output and insert it here. It should look similar to one below (replace it with your log inserted between triple ```):

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', 'https://www.youtube.com/watch?v=BYJEXJlHz4U']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2019.01.24
[debug] Python version 3.6.7 (CPython) - Linux-4.15.0-20-generic-x86_64-with-LinuxMint-19-tara
[debug] exe versions: ffmpeg N-47540-g90ac0e5f29-static, ffprobe 3.4.4
[debug] Proxy map: {}
...
<end of log>

Description of your issue, suggested solution and other information

Video can download, bug file name is '_-BYJEXJlHz4U.webm', instead '.-BYJEXJlHz4U.webm'
mabe it can named _. ?
https://www.youtube.com/watch?v=BYJEXJlHz4U

my english is poor