qt: Use correct conversion function for boost::path datadir

Fixes #9089.

src/qt/paymentserver.cpp

@@ -80,7 +80,7 @@ static QString ipcServerName()
     // Append a simple hash of the datadir
     // Note that GetDataDir(true) returns a different path
     // for -testnet versus main net
-    QString ddir(QString::fromStdString(GetDataDir(true).string()));
+    QString ddir(GUIUtil::boostPathToQString(GetDataDir(true)));
     name.append(QString::number(qHash(ddir)));
 
     return name;