Prevent crash when subscriber is invoked after view is destroyed.

app/src/main/java/org/thoughtcrime/securesms/stories/viewer/page/StoryViewerPageFragment.kt

@@ -31,6 +31,7 @@ import com.google.android.material.button.MaterialButton
 import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
 import io.reactivex.rxjava3.core.Observable
 import org.signal.core.util.DimensionUnit
+import org.signal.core.util.logging.Log
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.components.AvatarImageView
 import org.thoughtcrime.securesms.components.segmentedprogressbar.SegmentedProgressBar
@@ -334,6 +335,10 @@ class StoryViewerPageFragment :
         return@subscribe
       }
 
+      if (context == null) {
+        Log.d(TAG, "Subscriber called while fragment is detached. Ignoring state update.")
+      }
+
       if (state.posts.isNotEmpty() && state.selectedPostIndex in state.posts.indices) {
         val post = state.posts[state.selectedPostIndex]
 
@@ -936,6 +941,8 @@ class StoryViewerPageFragment :
   }
 
   companion object {
+    private val TAG = Log.tag(StoryViewerPageFragment::class.java)
+
     private val MAX_VIDEO_PLAYBACK_DURATION: Long = TimeUnit.SECONDS.toMillis(30)
     private val MIN_GIF_LOOPS: Long = 3L
     private val MIN_GIF_PLAYBACK_DURATION = TimeUnit.SECONDS.toMillis(5)