repo.Blame(path) does not accept folders

Reproduction steps

string relativePath = @"folder\anatherFolder\test.ts"
call repository.Blame(relativePath)
throws exception: "'the path 'folder\anatherFolder\test.ts' does not exist in the given tree"

Expected behavior

accept absolute or relative path
get all Hunks for file in path

Actual behavior

only accepts files in root directory of repository
throws exception: "'the path 'folder\anatherFolder\test.ts' does not exist in the given tree"

Version of LibGit2Sharp (release number or SHA1)

0.25.3

Operating system(s) tested; .NET runtime tested

.NET Core 2.1

从 repository.Blame(path) 入口开始，使用 LibGit2Sharp 0.25.3 和 .NET Core 2.1，通过嵌套路径 folder\anatherFolder\test.ts 重现该失败。跟踪路径的解析方式，然后验证 Blame 接受文件夹中的绝对路径和相对路径，并返回该文件的所有 hunk。