Fix usage of QString::toUtf8(). Fixes #2299

Desktop runtime has a couple bugs using already freed memory supplied to embedded python leading to occasional crashes and failures to start maintenance processes (VACUUM, ANALYZE, REINDEX, CLUSTER).

This is caused by incorrect usage of QString::toUtf8() which returns newly created QByteArray which is automatically destroyed once closing context; e.g.
Py_SetPythonHome(pythonHome.toUtf8().data());

runtime/Server.h

@@ -40,7 +40,12 @@ private:
 
     quint16  m_port;
     QString m_key;
+    // Application name in UTF-8 for Python
     wchar_t *m_wcAppName;
+    QByteArray PGA_APP_NAME_UTF8;
+    // PythonHome for Python
+    wchar_t *m_wcPythonHome;
+    QByteArray pythonHome_utf8;
 };
 
 #endif // SERVER_H