[BUG]: Specifying PageCount doesn't work if the query gets constructed with page number as the first query parameter

[corwin-gs]

What happened?

I tried requesting 5 pages of file changes in a PR, for example:

var apiOptions = new ApiOptions
{
    PageCount = 5,
};
var pullRequest = await GitHubClient.PullRequest.Get(repoOwnerName, repositoryName, pullRequestNumber);

which actually requests all pages.

This is because of this code in Pagination.cs

return uri.Query.Split('&')
    .Select(keyValue =>
    {
        var indexOf = keyValue.IndexOf('=');
        if (indexOf > 0)
        {
            var key = keyValue.Substring(0, indexOf);
            var value = keyValue.Substring(indexOf + 1);
            return new KeyValuePair<string, string>(key, value);
        }

        //just a plain old value, return it
        return new KeyValuePair<string, string>(keyValue, null);
    })
    .ToDictionary(x => x.Key, x => x.Value);

which incorrectly includes the initial ?, which you can see the effect of in this debugger screenshot

and TryGetValue naturally returns false.

Versions

Octokit.net 5.0.2

Relevant log output

No response

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