Fix crash with disposable lifecycle.

app/src/main/java/org/thoughtcrime/securesms/stories/viewer/first/StoryFirstTimeNavigationFragment.kt

@@ -52,6 +52,7 @@ class StoryFirstTimeNavigationFragment : DialogFragment(R.layout.story_viewer_fi
     view.callback = this
     viewModel.setIsDisplayingFirstTimeNavigation(true)
 
+    disposables.bindTo(viewLifecycleOwner)
     disposables += viewModel.state.observeOn(AndroidSchedulers.mainThread()).subscribe { state ->
       when (state.crossfadeSource) {
         is StoryViewerState.CrossfadeSource.ImageUri -> {