improvement: do not clear the commit filter while change the branch

- do not clear the commit filter while changing the branch
- do not change the filter if thereis `HEAD` filter while changing branch

src/ViewModels/Checkout.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Linq;
+using System.Threading.Tasks;
 
 namespace SourceGit.ViewModels
 {
@@ -102,7 +103,8 @@ public override async Task<bool> Sure()
             log.Complete();
 
             var b = _repo.Branches.Find(x => x.IsLocal && x.Name == Branch);
-            if (b != null && _repo.HistoriesFilterMode == Models.FilterMode.Included)
+            if (b != null && _repo.HistoriesFilterMode == Models.FilterMode.Included
+                && !_repo.Settings.HistoriesFilters.Any(f => f.Pattern == "HEAD"))
                 _repo.SetBranchFilterMode(b, Models.FilterMode.Included, true, false);
 
             _repo.MarkBranchesDirtyManually();

src/ViewModels/Repository.cs

@@ -1124,8 +1124,10 @@ public void SetBranchFilterMode(BranchTreeNode node, Models.FilterMode mode, boo
 
             if (clearExists)
             {
-                _settings.HistoriesFilters.Clear();
-                HistoriesFilterMode = Models.FilterMode.None;
+                _settings.HistoriesFilters.RemoveAll(_settings.HistoriesFilters
+                                                     .Where(f => f.Type != Models.FilterType.SoloCommits).ToArray());
+                if (_settings.HistoriesFilters.Count <= 0)
+                    HistoriesFilterMode = Models.FilterMode.None;
             }
 
             if (node.Backend is Models.Branch branch)