ensure that there is always a current user

this should also fix the app to start after it always crashed on startup because of https://github.com/nextcloud/talk-android/issues/2531

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

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

@@ -295,7 +295,7 @@ class ConversationsListController(bundle: Bundle) :
             }
             fetchRooms()
         } else {
-            Log.e(TAG, "currentUser was null in ConversationsListController.onAttach")
+            Log.e(TAG, "userManager.currentUser.blockingGet() returned null")
             Toast.makeText(context, R.string.nc_common_error_sorry, Toast.LENGTH_LONG).show()
         }
     }

app/src/main/java/com/nextcloud/talk/users/UserManager.kt

@@ -43,6 +43,7 @@ class UserManager internal constructor(private val userRepository: UsersReposito
     val currentUser: Maybe<User>
         get() {
             return userRepository.getActiveUser()
+                .switchIfEmpty(getAnyUserAndSetAsActive())
         }
 
     val currentUserObservable: Observable<User>