fix webuntis auth retry not working correctly

lib/api/webuntis/webuntisApi.dart

@@ -19,7 +19,7 @@ abstract class WebuntisApi extends ApiRequest {
   WebuntisApi(this.method, this.genericParam, {this.authenticatedResponse = true});
 
 
-  Future<String> query(WebuntisApi untis) async {
+  Future<String> query(WebuntisApi untis, {bool retry = false}) async {
     var query = '{"id":"ID","method":"$method","params":${untis._body()},"jsonrpc":"2.0"}';
 
     var sessionId = '0';
@@ -32,8 +32,9 @@ abstract class WebuntisApi extends ApiRequest {
     dynamic jsonData = jsonDecode(data.body);
     if(jsonData['error'] != null) {
       if(jsonData['error']['code'] == -8520) {
+        if(retry) throw WebuntisError('Authentication was tried (probably session timeout), but was not successful!', 1);
         await Authenticate.createSession();
-        this.query(untis);
+        return await this.query(untis, retry: true);
       } else {
         throw WebuntisError(jsonData['error']['message'], jsonData['error']['code']);
       }