Initialize the variable in the init_internals method

This will avoid that the conditional assignment is executed every time
has_query_constraints? is called.

activerecord/lib/active_record/persistence.rb

@@ -493,7 +493,7 @@ def query_constraints(*columns_list)
       end
 
       def has_query_constraints? # :nodoc:
-        @has_query_constraints ||= nil
+        @has_query_constraints
       end
 
       def query_constraints_list # :nodoc:
@@ -1140,6 +1140,7 @@ def init_internals
       super
       @_trigger_destroy_callback = @_trigger_update_callback = nil
       @previously_new_record = false
+      @has_query_constraints = false
     end
 
     def strict_loaded_associations