add more virtual methods for base handler

Pilz.Net/Api/Server/BaseHandler.cs

@@ -44,9 +44,11 @@ public abstract class BaseHandler<TEntity, TUpdateMsg>(IApiServer server)
     {
         if (!server.Manager.Find(id, out TEntity? entity))
             return ApiResult.NotFound();
-        if (UpdateEntity(new(entity, msg, req)) is ApiResult result)
+        var update = new EntityUpdate(entity, msg, req);
+        if (UpdateEntity(update) is ApiResult result)
             return result;
-        server.Manager.Save(entity, true);
+        if (OnSave(update) is ApiResult result2)
+            return result2;
         return ToClient(entity).ToItemResult();
     }
 
@@ -63,7 +65,11 @@ public abstract class BaseHandler<TEntity, TUpdateMsg>(IApiServer server)
         return null;
     }
 
-    protected virtual ApiResult? OnSave(TEntity entity, TUpdateMsg update)
+    protected virtual ApiResult? OnSave(EntityUpdate update)
+    {
+        server.Manager.Save(update.Entity, true);
+        return null;
+    }
 
     protected virtual TEntity CreateNewEntity(TUpdateMsg msg)
     {