desktop-shell: Properly set the shsurf output to that of the view
The shell_surface is (initially) being assigned the default output and it case it starts on a different ouput, or is being moved there, it it not be updated to the correct output of the view.
This will break the stacking order of the views by having a fullscreen view, which will never be demoted a lower stacking order due to newer non-fullscreen view which will have the shell_surface output set to the default one. Doing so will ignore the fullscreen view when determining which view should should be demoted a lower stacking order.
This is only seen in multiple output configuration.
Signed-off-by: Marius Vlad firstname.lastname@example.org