Qt v5.15 compatibility

Network/LotWUsers.cpp

@@ -69,11 +69,13 @@ public:
 
   void download (QUrl url)
   {
+#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)
     if (QNetworkAccessManager::Accessible != network_manager_->networkAccessible ())
       {
         // try and recover network access for QNAM
         network_manager_->setNetworkAccessible (QNetworkAccessManager::Accessible);
       }
+#endif
 
     QNetworkRequest request {url};
     request.setRawHeader ("User-Agent", "WSJT LotW User Downloader");