pukkandan 337e0c62f8 [embedthumbnail] Correctly escape filename ...

Closes #352
The approach in [1] is faulty as can be seen in the test cases
1. https://github.com/ytdl-org/youtube-dl/commit/bff857a8af696e701482208617bf0b7564951326

2021-05-29 02:31:14 +05:30

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cookies

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f4m

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ism

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m3u8

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mpd

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thumbnails/foo %d bar

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xspf

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