Fix crash when rotating device in emoji reaction picker.

Adds null check for selectedConversationModel in hideInternal() to
prevent NPE when hide() is called after the overlay has already been
hidden during configuration changes.

Fixes #14491

app/src/main/java/org/thoughtcrime/securesms/conversation/ConversationReactionOverlay.java

@@ -407,6 +407,10 @@ public final class ConversationReactionOverlay extends FrameLayout {
   }
 
   private void hideInternal(@Nullable OnHideListener onHideListener) {
+    if (overlayState == OverlayState.HIDDEN || selectedConversationModel == null) {
+      return;
+    }
+
     overlayState = OverlayState.HIDDEN;
 
     AnimatorSet animatorSet = newHideAnimatorSet();