fix crash when navigating back from chat to conversation list

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

app/src/main/java/com/nextcloud/talk/activities/MainActivity.kt

@@ -202,7 +202,7 @@ class MainActivity : BaseActivity(), ActionBarProvider {
     fun resetConversationsList() {
         userManager.users.subscribe(object : SingleObserver<List<User>> {
             override fun onSubscribe(d: Disposable) {
-                TODO("Not yet implemented")
+                // unused atm
             }
 
             override fun onSuccess(users: List<User>) {