AbstractWaylandOutput: always emit mode change when mode is set

Otherwise there can be situations where the platform sets a mode but
KScreen never gets notified of it.

src/abstract_wayland_output.cpp

@@ -233,6 +233,7 @@ void AbstractWaylandOutput::setCurrentModeInternal(const QSize &size, int refres
         m_modeSize = size;
         m_refreshRate = refreshRate;
 
+        Q_EMIT currentModeChanged();
         if (sizeChanged) {
             Q_EMIT geometryChanged();
         }