enhance: prevent to start bisect if it is already running

Signed-off-by: leo <longshuang@msn.cn>

Author: love-linger

src/Views/RepositoryToolbar.axaml.cs

@@ -124,6 +124,8 @@ private void StartBisect(object sender, RoutedEventArgs e)
             {
                 if (repo.LocalChangesCount > 0)
                     App.RaiseException(repo.FullPath, "You have un-committed local changes. Please discard or stash them first.");
+                else if (repo.IsBisectCommandRunning || repo.BisectState != Models.BisectState.None)
+                    App.RaiseException(repo.FullPath, "Bisect is running! Please abort it before starting a new one.");
                 else
                     repo.Bisect("start");
             }