dbhub: Fix possible crash

This fixes a crash that occurs if there is an error while fetching
something other than a database and no database has been downloaded
before, e.g. when getting the root directory listing fails.

src/RemoteDatabase.cpp

@@ -238,7 +238,8 @@ void RemoteDatabase::gotError(QNetworkReply* reply, const QList<QSslError>& erro
     QMessageBox::warning(0, qApp->applicationName(), message);
 
     // Delete reply later, i.e. after returning from this slot function
-    m_progress->reset();
+    if(m_progress)
+        m_progress->reset();
     reply->deleteLater();
 }