The 'current generators' dialog has a page for each generator. The choice of which of these pages is visible when the dialog is first opened seems to be random (or at least I don't see the pattern). This patch makes sure that the currently running generator determines which page is opened, because in most cases people will want to set preferences for the generator they are currently using.
Unfortunately, I had to change the interface of Okular::ConfigInterface for this. Speak up if you know a better way.