bradient: perhaps fall back to application name if there's no window title

If you run

qml something.qml

where something.qml has an Item (or Rectangle etc.) as the root object, the default window title will change to "Qml Runtime".  But on Wayland with default bradient decorations, it ends up being blank.

This string seems to exist only in tools/qml/main.cpp

app->setApplicationName("Qml Runtime");

so I guess it must be a typical window manager feature on X11: at least Gnome and Openbox will use use it instead of leaving the title empty.