examples: fix qt demo to work without STL support

The function toStdString() is only available when QT was
compiled with STL support. The configure script does
not check STL support and might build the QT examples
even if toStdString() is not available.

Fix this, by not using the function.

https://bugzilla.gnome.org/show_bug.cgi?id=727608

Signed-off-by: Thomas Haller <thaller@redhat.com>

examples/C/qt/monitor-nm-running.cpp

@@ -51,13 +51,13 @@ class NMWatcher: public QObject {
 
 void NMWatcher::serviceRegistered(const QString& name)
 {
-    std::cout << "Name '" << name.toStdString() << "' registered"
+    std::cout << "Name '" << name.constData() << "' registered"
               << " => NM is running" << std::endl;
 }
 
 void NMWatcher::serviceUnregistered(const QString& name)
 {
-    std::cout << "Name '" << name.toStdString() << "' unregistered"
+    std::cout << "Name '" << name.constData() << "' unregistered"
               << " => NM is not running" << std::endl;
 }