fix text encoding in qt4 under Linux (bug #49118)

* octave-gui.cc (gui_application::execute): For Qt4, restore call to
QTextCodec::setCodecForCStrings that was removed in changeset
2fd4f1a3f4a8.

Author: Hartmut Gimpel

libgui/src/octave-gui.cc

@@ -159,6 +159,10 @@ namespace octave
     QTextCodec::setCodecForLocale (QTextCodec::codecForName ("UTF-8"));
 #endif
 
+#if defined (HAVE_QT4)
+    QTextCodec::setCodecForCStrings (QTextCodec::codecForName ("UTF-8"));
+#endif
+
     // set windows style for windows
 #if defined (Q_OS_WIN32)
     qt_app.setStyle(QStyleFactory::create("Windows"));