Improve empty country removal logic (#2731)

Countries are now removed only if they have no monarch, no territories,
and no pre-Imperator rulers (defined in
configurables/characters_prehistory.txt).

Author: IhateTrains

ImperatorToCK3/Imperator/World.cs

@@ -331,10 +331,10 @@ public World(Configuration config, ConverterVersion converterVersion, out Thread
 		Logger.Info("Linking Countries with Families...");
 		Countries.LinkFamilies(Families);
 
-		RemoveEmptyCountries();
-
 		LoadPreImperatorRulers();
 
+		RemoveEmptyCountries();
+
 		// Detect specific mods.
 		InvictusDetected = GlobalFlags.Contains("is_playing_invictus");
 		TerraIndomitaDetected = Countries.Any(c => c.Variables.Contains("unification_points")) ||
@@ -404,8 +404,8 @@ private void ParseSave(Configuration config, ConverterVersion converterVersion,
 	}
 
 	private void RemoveEmptyCountries() {
-		// Drop countries with no monarch and no territories.
-		int count = Countries.RemoveAll(country => country is {Monarch: null, TerritoriesCount: 0});
+		// Drop countries with no monarch, no territories and no pre-Imperator rulers.
+		int count = Countries.RemoveAll(c => c is {Monarch: null, TerritoriesCount: 0, RulerTerms.Count: 0});
 		if (count > 0) {
 			Logger.Info($"Removed {count} empty countries.");
 		}