Fix invalid liege entries in title history (#2166)

Author: IhateTrains

ImperatorToCK3/CK3/Characters/CharacterCollection.cs

@@ -535,7 +535,7 @@ public void PurgeUnneededCharacters(Title.LandedTitles titles, DynastyCollection
 		dynasties.FlattenDynastiesWithNoFounders(this, houses, ck3BookmarkDate);
 
 		// Clean up title history.
-		titles.RemoveInvalidHoldersFromHistory(this);
+		titles.CleanUpHistory(this, ck3BookmarkDate);
 	}
 
 	public void RemoveEmployerIdFromLandedCharacters(Title.LandedTitles titles, Date conversionDate) {

ImperatorToCK3/CK3/Titles/LandedTitles.cs

@@ -257,7 +257,7 @@ public ImmutableHashSet<string> GetAllHolderIds() {
 			return this.SelectMany(t => t.GetAllHolderIds()).ToImmutableHashSet();
 		}
 
-		public void RemoveInvalidHoldersFromHistory(CharacterCollection characters) {
+		public void CleanUpHistory(CharacterCollection characters, Date ck3BookmarkDate) {
 			Logger.Debug("Removing invalid holders from history...");
 
 			var validIds = characters.Select(c => c.Id).ToImmutableHashSet();
@@ -270,6 +270,31 @@ public void RemoveInvalidHoldersFromHistory(CharacterCollection characters) {
 					value => value.ToString() is string valStr && valStr != "0" && !validIds.Contains(valStr)
 				);
 			}
+			
+			// Remove liege entries that are not valid (liege title is not held at the entry date).
+			foreach (var title in this) {
+				if (!title.History.Fields.TryGetValue("liege", out var liegeField)) {
+					continue;
+				}
+
+				foreach (var (date, entriesList) in liegeField.DateToEntriesDict.ToArray()) {
+					if (entriesList.Count == 0) {
+						continue;
+					}
+					
+					var lastEntry = entriesList.Last();
+					var liegeTitleId = lastEntry.Value.ToString();
+					if (liegeTitleId is null || liegeTitleId == "0") {
+						continue;
+					}
+
+					if (!TryGetValue(liegeTitleId, out var liegeTitle)) {
+						liegeField.DateToEntriesDict.Remove(date);
+					} else if (liegeTitle.GetHolderId(date) == "0") {
+						liegeField.DateToEntriesDict.Remove(date);
+					}
+				}
+			}
 		}
 
 		public void ImportImperatorCountries(