FIx failing tests.

Author: grokys

src/GitHub.InlineReviews/ViewModels/InlineCommentPeekViewModel.cs

@@ -192,7 +192,7 @@ async Task UpdateThread()
 
             if (!string.IsNullOrWhiteSpace(placeholderBody))
             {
-                var placeholder = Thread.Comments.LastOrDefault();
+                var placeholder = vm.Comments.LastOrDefault();
 
                 if (placeholder?.EditState == CommentEditState.Placeholder)
                 {

test/GitHub.InlineReviews.UnitTests/ViewModels/InlineCommentPeekViewModelTests.cs

@@ -370,6 +370,7 @@ IPeekSession CreatePeekSession()
         IPullRequestSession CreateSession()
         {
             var result = Substitute.For<IPullRequestSession>();
+            result.PullRequest.Returns(new PullRequestDetailModel());
             result.User.Returns(new ActorModel { Login = "CurrentUser" });
             result.LocalRepository.CloneUrl.Returns(new UriString("https://foo.bar"));
             return result;