fix: Login multiple accounts after another

lib/widgets/matrix.dart

@@ -140,6 +140,7 @@ class MatrixState extends State<Matrix> with WidgetsBindingObserver {
           .where((l) => l == LoginState.loggedIn)
           .first
           .then((_) {
+        _loginClientCandidate = null;
         widget.clients.add(_loginClientCandidate);
         ClientManager.addClientNameToStore(_loginClientCandidate.clientName);
         _registerSubs(_loginClientCandidate.clientName);