That's exactly what I think is the wrong way of doing this. If you have already set your root password or don't want to change your current one, you should be able to abort this dialog without retyping your current password.

I think the best solution would be one more dialog that asks at first whether you want to change your password or not. Or the password dialog could be extended by a cancel button. The Info text should mention that cancel will abort password change without aborting the setup.