std.net.curl: fix maxRedirects() interpretation of uint.max

[foutaise]

maxRedirects(uint maxRedirs) specify in its documentation string that uint.max can be used for infinite redirection.

But in the code, when a uint.max value is used, redirects are disabled, by setting CurlOption.followlocation to 0.

This PR switch off redirection if maxRedirs is equal to 0, and allow redirections up to maxRedirs otherwise.

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[CyberShadow]

As this would be a breaking change, I think improving the documentation is the correct action here.

[foutaise]

As this would be a breaking change, I think improving the documentation is the correct action here.

I'm afraid you're right. Something like this?

Set max allowed redirections using the location header.
uint.max to disable redirections.