Reply a meaningful dBus error when detecting unmanaged windows
Currently, the method createErrorReply()
with empty strings
errors out and the client gets no answer:
QDBusConnection: error: could not send error message to service "": Error name cannot be empty
Simple test:
qdbus org.kde.KWin /KWin org.kde.KWin.showDebugConsole
qdbus org.kde.KWin /KWin org.kde.KWin.queryWindowInfo
Error name uses D-Bus Interface-like notation as suggested in https://doc.qt.io/qt-5/qdbuserror.html#name