[Bug]Fix pagination when ApiOptions.StartPage is explicitly set.

[pkindruk]

Resolves #1955, #2602

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Before the change?

• Following code never returns a list of release and hits API rate limit:

var client = new GitHubClient(new ProductHeaderValue("Test"));
var releases = await client.Repository.Release.GetAll("octokit", "octokit.net",
        new ApiOptions { StartPage = 1, PageSize = 10, PageCount = 2 });

• Looks like any method prefixed with GetAll* is affected when called with ApiOptions.StartPage != null specified and one of the following is true:
  • ApiOptions.PageCount > 1
  • ApiOptions.PageCount == null

After the change?

• Example code returns 20 releases as expected

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[nickfloyd]

Thank you for knocking this out @pkindruk ❤️