Fix crashes and issues with blurred avatars.

- Tinting on Android 5/6 caused NPE deep in Android
- Invite group flow can have zero members
- Missed spot to blur avatar in old notification flow

app/src/main/res/layout/conversation_banner_view.xml

@@ -22,7 +22,8 @@
         android:layout_height="0dp"
         android:orientation="vertical"
         android:gravity="center"
-        android:visibility="gone"
+        android:background="@drawable/circle_tint_darker"
+        android:visibility="visible"
         android:foreground="?attr/selectableItemBackground"
         app:layout_constraintBottom_toBottomOf="@+id/message_request_avatar"
         app:layout_constraintEnd_toEndOf="@+id/message_request_avatar"