enhance: disable checkout branch via double-clicking branch tree node (#899)

Author: love-linger

src/ViewModels/Repository.cs

@@ -1062,6 +1062,9 @@ public void CheckoutBranch(Models.Branch branch)
                 }
             }
 
+            if (IsBare)
+                return;
+
             if (!CanCreatePopup())
                 return;