Ensure there is a fragment manager to use.

- Fixes Play Store reported java.lang.NullPointerException in
com.battlelancer.seriesguide.ui.dialogs.ListsDialogFragment.showListsDialog.
Ensure there is a fragment manager when finished connecting trakt.

- Fixes Play Store reported java.lang.NullPointerException
in
com.battlelancer.seriesguide.ui.ConnectTraktCredentialsFragment$2$1.onPostExecu....
Save add page count, notify viewpager if it changes.

- trakt credentials could get invalidated while user is within add
activity changing the page count. However, we did not notify ViewPager
about it which made him very unhappy.
- Fixes Play Store reported java.lang.IllegalStateException in
android.support.v4.view.ViewPager.populate.