Avoid NPE in setupSwipeToReply

Exception java.lang.NullPointerException:
  at com.nextcloud.talk.controllers.ChatController.setupSwipeToReply (ChatController.kt:419)
  at com.nextcloud.talk.controllers.ChatController.access$setupSwipeToReply (ChatController.kt:221)
  at com.nextcloud.talk.controllers.ChatController$getRoomInfo$1.onNext (ChatController.kt:378)
  at com.nextcloud.talk.controllers.ChatController$getRoomInfo$1.onNext (ChatController.kt:362)
  at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.drainNormal (ObservableObserveOn.java:201)
  at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.run (ObservableObserveOn.java:255)
  at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run (HandlerScheduler.java:124)
  at android.os.Handler.handleCallback (Handler.java:883)
  at android.os.Handler.dispatchMessage (Handler.java:100)
  at android.os.Looper.loop (Looper.java:237)
  at android.app.ActivityThread.main (ActivityThread.java:7830)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:492)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1040)

Signed-off-by: Marcel Hibbe <dev@mhibbe.de>

app/src/main/java/com/nextcloud/talk/controllers/ChatController.kt

@@ -415,18 +415,20 @@ class ChatController(args: Bundle) :
             participantPermissions.hasChatPermission() &&
             !isReadOnlyConversation()
         ) {
-            val messageSwipeController = MessageSwipeCallback(
-                activity!!,
-                object : MessageSwipeActions {
-                    override fun showReplyUI(position: Int) {
-                        val chatMessage = adapter?.items?.get(position)?.item as ChatMessage?
-                        replyToMessage(chatMessage)
+            activity?.let {
+                val messageSwipeController = MessageSwipeCallback(
+                    it,
+                    object : MessageSwipeActions {
+                        override fun showReplyUI(position: Int) {
+                            val chatMessage = adapter?.items?.get(position)?.item as ChatMessage?
+                            replyToMessage(chatMessage)
+                        }
                     }
-                }
-            )
+                )
 
-            val itemTouchHelper = ItemTouchHelper(messageSwipeController)
-            itemTouchHelper.attachToRecyclerView(binding?.messagesListView)
+                val itemTouchHelper = ItemTouchHelper(messageSwipeController)
+                itemTouchHelper.attachToRecyclerView(binding?.messagesListView)
+            }
         }
     }