code_style: remove Rider warnings

Signed-off-by: leo <[email protected]>

Author: love-linger

src/ViewModels/CommitDetail.cs

@@ -196,7 +196,7 @@ public void ViewRevisionFile(Models.Object file)
                                 var stream = Commands.QueryFileContent.Run(_repo.FullPath, _commit.SHA, file.Path);
                                 var fileSize = stream.Length;
                                 var bitmap = fileSize > 0 ? new Bitmap(stream) : null;
-                                var imageType = Path.GetExtension(file.Path).TrimStart('.').ToUpper(CultureInfo.CurrentCulture);
+                                var imageType = ext!.Substring(1).ToUpper(CultureInfo.CurrentCulture);
                                 var image = new Models.RevisionImageFile() { Image = bitmap, FileSize = fileSize, ImageType = imageType };
                                 Dispatcher.UIThread.Invoke(() => ViewRevisionFileContent = image);
                             }

src/ViewModels/Histories.cs

@@ -153,12 +153,9 @@ public void Select(IList commits)
             }
             else if (commits.Count == 1)
             {
-                var commit = commits[0] as Models.Commit;
-
+                var commit = (commits[0] as Models.Commit)!;
                 if (_repo.SearchResultSelectedCommit == null || _repo.SearchResultSelectedCommit.SHA != commit.SHA)
-                {
                     _repo.SearchResultSelectedCommit = _repo.SearchedCommits.Find(x => x.SHA == commit.SHA);
-                }
 
                 AutoSelectedCommit = commit;
                 NavigationId = _navigationId + 1;
@@ -224,7 +221,7 @@ public void DoubleTapped(Models.Commit commit)
         public ContextMenu MakeContextMenu(ListBox list)
         {
             var current = _repo.CurrentBranch;
-            if (current == null)
+            if (current == null || list.SelectedItems == null)
                 return null;
 
             if (list.SelectedItems.Count > 1)