Fix race condition allowing to run several instances of qBittorrent at the same time

src/misc.h

@@ -122,6 +122,7 @@ public:
   // Take a number of seconds and return an user-friendly
   // time duration like "1d 2h 10m".
   static QString userFriendlyDuration(qlonglong seconds);
+  static QString getUserIDString();
 
   // Convert functions
   static QStringList toStringList(const QList<bool> &l);