window-wayland: Make sure the size of the buffer rect is kept up to date

When we changed the setting of the buffer rect to be inside the moving
code to make sure it was updated in places we were moving directly
without any round-trip needed, I removed a code to set the buffer rect
without remembering that's where the size of it was updated.

Add back the code to update the buffer rect.

This fixes Wayland windows not appearing.