scene: Fix syncing buffer source box with 100% scale

The buffer source box is synchronized when the surface-to-buffer matrix
changes. However, when using 100% scaling, it's likely that the
surface-to-buffer matrix will be identity and therefore no corresponding
signal to indicate the change will be emitted.

To fix that, we need to update the buffer source box also when the
buffer size changes.

src/scene/surfaceitem_wayland.cpp

@@ -91,6 +91,7 @@ void SurfaceItemWayland::handleSurfaceSizeChanged()
 
 void SurfaceItemWayland::handleBufferSizeChanged()
 {
+    setBufferSourceBox(m_surface->bufferSourceBox());
     setBufferSize(m_surface->bufferSize());
     discardPixmap();
 }