Fix a bug in chat that caused crash when leaving sometimes

Signed-off-by: Mario Danic <mario@lovelyhq.com>

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

@@ -909,7 +909,9 @@ public class ChatController extends BaseController implements MessagesListAdapte
                     }
                 }
 
-                adapter.addToEnd(chatMessageList, false);
+                if (adapter != null) {
+                    adapter.addToEnd(chatMessageList, false);
+                }
 
             } else {