shell.c: Set dirty for visible views on destroyed output
shell.c: Set dirty for visible views on destroyed output

The geometry for visible views will keep unchanged,
weston_view_set_position() doesn't mark these views
as dirty. So there is no chance for them to reassign output, then
these views will disappear.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=72946

Signed-off-by: Xiong Zhang <887154684953c1d7bc9f653d05b20c8de98c15bc@intel.com>

udoprog/weston,eyolfson/weston,krezovic/weston,xorgy/weston,giucam/weston,xorgy/weston,sir-murray/weston,Gnurou/weston,mchalupa/weston,krezovic/weston,eyolfson/weston,udoprog/weston,sir-murray/weston,Tarnyko/weston-xdg_surface_present,mchalupa/weston,Fantu/compositor-spice,Fantu/compositor-spice,kwm81/weston,jonnylamb/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,Gnurou/weston,kwm81/weston,jonnylamb/weston,giucam/weston