fix: NRE on commit double-click

Author: gadfly3173

src/ViewModels/Histories.cs

@@ -242,37 +242,27 @@ public async Task<bool> CheckoutBranchByDecoratorAsync(Models.Decorator decorato
 
         public async Task CheckoutBranchByCommitAsync(Models.Commit commit)
         {
+            if (commit == null)
+                return;
+
             if (commit.IsCurrentHead)
                 return;
 
             Models.Branch firstRemoteBranch = null;
             foreach (var d in commit.Decorators)
             {
-                if (d.Type == Models.DecoratorType.LocalBranchHead)
-                {
-                    var b = _repo.Branches.Find(x => x.Name == d.Name);
-                    if (b == null)
-                        continue;
-
-                    await _repo.CheckoutBranchAsync(b);
-                    return;
-                }
-
-                if (d.Type == Models.DecoratorType.RemoteBranchHead)
+                if (d.Type == Models.DecoratorType.LocalBranchHead || d.Type == Models.DecoratorType.RemoteBranchHead)
                 {
-                    var rb = _repo.Branches.Find(x => x.FriendlyName == d.Name);
-                    if (rb == null)
-                        continue;
+                    var handled = await CheckoutBranchByDecoratorAsync(d);
+                    if (handled)
+                        return;
 
-                    var lb = _repo.Branches.Find(x => x.IsLocal && x.Upstream == rb.FullName);
-                    if (lb.Ahead.Count == 0)
+                    if (d.Type == Models.DecoratorType.RemoteBranchHead)
                     {
-                        if (_repo.CanCreatePopup())
-                            _repo.ShowPopup(new CheckoutAndFastForward(_repo, lb, rb));
-                        return;
+                        var rb = _repo.Branches.Find(x => x.FriendlyName == d.Name);
+                        if (rb != null && firstRemoteBranch == null)
+                            firstRemoteBranch = rb;
                     }
-
-                    firstRemoteBranch ??= rb;
                 }
             }