The lines you have proposed changing should not prevent the restrict moderators function from working correctly
The MoveTopicAllowed variable is used to restrict the forums displayed in the combobox, your changes will actually prevent the combobox from appearing, rather than affect its content
Maybe if you explain why you think it isn't working, we will take a look, but since this code hasn't changed in quite sometime, I'm pretty sure we would have noticed here if it was a problem.
Yes, you're right. My changes hides combobox when "Restrict moderators..." option is enabled. In this case combobox displays only one item, so you can replace it with hidden form field.