Prevent iOS crash when redirect url is null

[rmartin48]

PR Checklist

• The PR title follows our guidelines: https://github.com/proyecto26/react-native-inappbrowser/blob/main/CONTRIBUTING.md#pull-request-process.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• All existing tests are passing
• Tests for the changes are included

What is the current behavior?

On iOS, calling openAuth with undefined/null for redirectUrl will crash the app. This issue was recently introduced in this commit where the scheme is being extracted from the redirect url. The result is that escapedRedirectURL = "<null>" which is not a valid URL scheme.

ExceptionsManager.js:179 Exception '*** -[NSURL initWithString:relativeToURL:]: nil string parameter' was thrown while invoking openAuth on target RNInAppBrowser with params (
    "https://xxx.xxx.amazoncognito.com/logout?client_id=xxx&logout_uri=myscheme%3A%2F%2Fpath",
    "<null>",
       ...

What is the new behavior?

Don't attempt to extract the scheme from redirectUrl if it is undefined. Simply pass in nil which will be handled gracefully.

[jdnichollsc]

Why redirectUrl is null? I mean, this parameter is not optional 🤔

[jdnichollsc]

I'm asking because that url is required for Android platform as you can see here https://github.com/proyecto26/react-native-inappbrowser/blob/develop/utils.js#L31

[deermichel]

I don't know why it's null, but we encounter the same crashes on iOS 👍🏽

[jdnichollsc]

Please create an issue related to this PR and attach a reproducible demo to understand better your scenario 👍

[jdnichollsc]

Thanks for your contribution mate! <3