Ensure.HandleError does not set GitErrorCategory.

Reproduction steps

This reproduces with any error handled by Ensure.HandleError, but my exact repro steps are:

1. Clone repository
2. Commit
3. Push with credentials that have only read permissions to the repo.

Looking at the error message, the error appears to be thrown from here.

Expected behavior

Exception is thrown and the ex.Data["libgit2.category"] is set to a proper value. In my case it would be GitErrorCategory.Net.

Actual behavior

Exception is thrown, but the ex.Data["libgit2.category"] has value -1.

Version of LibGit2Sharp (release number or SHA1)

0.26.2

Operating system(s) tested; .NET runtime tested

Windows 10 1909; NET 4.6.1

从 LibGit2Sharp/Core/Ensure.cs 中的 Ensure.HandleError 开始，并与 libgit2 的 src/transports/winhttp.c 中提到的原生错误路径进行比较。在 Windows 上复现只读 push，并检查 ex.Data["libgit2.category"] 是如何赋值的。当此路径报告 GitErrorCategory.Net 而不是 -1 时，即表示完成。