Fix share PDF download when redirect shows captcha

[mvasilak]

Solves zotero/zotero#3526 for iOS

[michalrentka]

@mvasilak is this completed? You're pretty much showing webview for all redirects. Based on zotero/zotero#3526 there are conditions to meet before we show the web view?

[mvasilak]

There is a guard just before to limit it for sciencedirect, which in zotero/zotero#3526 takes place in https://github.com/zotero/zotero/blob/ba86e9b4c92aea8818e50d96b04f905721f66162/chrome/content/zotero/xpcom/browserDownload.js#L178

The workflow is a bit different, as in iOS we handle a successful download where the file is not the expected PDF, while desktop handles an exception, but the end result is the same.

You are right though, we can improve by not showing the web view, even momentarily, when the redirect could work, as the cookie may be cached from a previous save. I'll make this improvement.

Is there any other point that you have noticed missing?

[michalrentka]

Original ticket also mentions Matches the HiddenBrowser loaded HTML page for a captcha element., so I'd probably add that too so that we're on the same page.

[mvasilak]

@michalrentka ready for another look