Add using to avoid crash in Release mode

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

Author: jcansdale

src/GitHub.App/Services/PullRequestService.cs

@@ -14,8 +14,8 @@
 using System.Reactive;
 using System.Collections.Generic;
 using LibGit2Sharp;
-using System.Diagnostics;
 using GitHub.Logging;
+using Serilog;
 
 namespace GitHub.Services
 {
@@ -102,9 +102,14 @@ public IObservable<IReadOnlyList<CommitMessage>> GetMessagesForUniqueCommits(
 
         public IObservable<bool> IsWorkingDirectoryClean(ILocalRepositoryModel repository)
         {
-            var repo = gitService.GetRepository(repository.LocalPath);
-            var isClean = !IsFilthy(repo.RetrieveStatus());
-            return Observable.Return(isClean);
+            // The `using` appears to resolve this issue:
+            // https://github.com/github/VisualStudio/issues/1306
+            using (var repo = gitService.GetRepository(repository.LocalPath))
+            {
+                var status = repo.RetrieveStatus();
+                var isClean = !IsFilthy(status);
+                return Observable.Return(isClean);
+            }
         }
 
         static bool IsFilthy(RepositoryStatus status)
@@ -271,7 +276,7 @@ public IObservable<Unit> SwitchToBranch(ILocalRepositoryModel repository, IPullR
                 var repo = gitService.GetRepository(repository.LocalPath);
                 var branchName = GetLocalBranchesInternal(repository, repo, pullRequest).FirstOrDefault();
 
-                Log.Assert(branchName != null, "PullRequestService.SwitchToBranch called but no local branch found");
+                Logging.Log.Assert(branchName != null, "PullRequestService.SwitchToBranch called but no local branch found");
 
                 if (branchName != null)
                 {