Add using to avoid crash in Release mode

[jcansdale]

Somehow putting the repo object in a using avoids the following issue: #1306

Fixes #1306

[jcansdale]

@ethomson, any idea why simply adding using statement might prevent a crash that only occurs when compiled in Release mode? I'm very confused!

Here is where the crash was happening:

Sometimes it would manifest itself like this:

LibGit2Sharp.NotFoundException: no submodule named 'submodules/splat'
   at LibGit2Sharp.Core.Ensure.HandleError(Int32 result)
   at LibGit2Sharp.Core.Proxy.git_status_list_new(RepositoryHandle repo, GitStatusOptions options)
   at LibGit2Sharp.RepositoryStatus..ctor(Repository repo, StatusOptions options)
   at LibGit2Sharp.RepositoryExtensions.RetrieveStatus(IRepository repository)
   at GitHub.Services.PullRequestService.IsWorkingDirectoryClean(ILocalRepositoryModel repository) in C:\source\github.com\github\VisualStudio\src\GitHub.App\Services\PullRequestService.cs:line 108
   at GitHub.ViewModels.PullRequestDetailViewModel.<Load>d__100.MoveNext() in C:\source\github.com\github\VisualStudio\src\GitHub.App\ViewModels\PullRequestDetailViewModel.cs:line 439

[jcansdale]

Confirmation from @awbushnell that this fix works. 👍

@jcansdale Yes!! I have installed the vsix to both Visual Studio 2015 and Visual Studio 2017 on my local system and in both cases, I have been opening pull requests inside the respective IDE, and no crashes etc. seem to be occurring... Let me know when it is "officially" released to the public and I can get our teams updating to it locally

[grokys]

Approving this because it fixes the crash - it would be nice to know why though!