[downloader/external] Fix WgetFD proxy

[coletdjnz]

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From ytdl-org/youtube-dl#29343

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

wget --proxy argument accepts a bool for enable/disabling the proxy, not for setting what proxy to use.

so before it was sending the proxy url as a normal url to download...

see ytdl-org/youtube-dl#29343 for more details