Fix exception while cleaning up title history (#2786) #patch

Replaces Min with OrderBy and FirstOrDefault to select the next valid
liege holder date. This improves clarity and ensures correct handling
when no suitable date is found.

Author: IhateTrains

ImperatorToCK3/CK3/Titles/LandedTitles.cs

@@ -494,7 +494,9 @@ public void CleanUpHistory(CharacterCollection characters, Date ck3BookmarkDate)
 						liegeTitle.History.Fields.TryGetValue("holder", out var liegeHolderField);
 						Date? laterDate = liegeHolderField?.DateToEntriesDict
 							.Where(kvp => kvp.Key > date && kvp.Key <= ck3BookmarkDate && kvp.Value.Count != 0 && kvp.Value[^1].Value.ToString() != "0")
-							.Min(kvp => kvp.Key);
+							.OrderBy(kvp => kvp.Key)
+							.Select(kvp => (Date?)kvp.Key)
+							.FirstOrDefault(defaultValue: null);
 
 						if (laterDate == null) {
 							liegeField.DateToEntriesDict.Remove(date);