Remotes are sometimes not returned for worktree

Reproduction steps

1. Create repository with remote and commit.
2. Create branch and create a worktree from that branch.
3. Copy the path to worktree and run the following code:

var worktreePath = "Here is your worktree path";
var repositoryPath = Repository.Discover(worktreePath);
var repo = new Repository(repositoryPath);

var before = repo.Network.Remotes.ToArray();
_ = repo.Head.RemoteName;
var after = repo.Network.Remotes.ToArray();

Expected behavior

Both before and after variable contain remote.

Actual behavior

The before variable contains remote, after is empty.

Version of LibGit2Sharp (release number or SHA1)

Latest master: 7f59d22c4fdb7b3d14511aca567e64eefaa43ab2

Operating system(s) tested; .NET runtime tested

Windows, .NET Framework 462 and .NET Core 2.1. I believe it doesn't matter.

首先在最新的 master 上运行报告中的 C# 复现，重点关注使用关联 worktree 时的 Repository.Discover、repo.Network.Remotes 和 repo.Head.RemoteName。跟踪访问 Head.RemoteName 为什么会改变 remotes 的结果；当访问前后都包含该 repository remote 时即完成。