Fix Preloader to not generate a query for already loaded association with query_constraints (#1150)

Author: aidanharan

lib/active_record/connection_adapters/sqlserver/core_ext/preloader.rb

@@ -10,6 +10,8 @@ module LoaderQuery
           def load_records_for_keys(keys, &block)
             return super unless scope.connection.sqlserver?
 
+            return [] if keys.empty?
+
             if association_key_name.is_a?(Array)
               query_constraints = Hash.new { |hsh, key| hsh[key] = Set.new }