Fix a bug with conversation info disappearing

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

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

@@ -203,7 +203,9 @@ public class ConversationInfoController extends BaseController {
 
         setupAdapter();
 
-        participantsListCategory.setVisibility(View.VISIBLE);
+        if (participantsListCategory != null) {
+            participantsListCategory.setVisibility(View.VISIBLE);
+        }
         adapter.notifyDataSetChanged();
     }