src/shell.c: set black_surface->width and height

full screen black_surface doesn't have associated wl_buffer, so
black_surface->width and height can't get value through
weston_surface_commit(). then weston_surface_damage(black_surface)
will be wrong in shell_stack_fullscreen(), the result is that we
can't see a full screen view whe APP window's size isn't equal to
output's size like running weston-gears

Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>

src/shell.c

@@ -2254,6 +2254,8 @@ create_black_surface(struct weston_compositor *ec,
 	pixman_region32_init_rect(&surface->opaque, 0, 0, w, h);
 	pixman_region32_fini(&surface->input);
 	pixman_region32_init_rect(&surface->input, 0, 0, w, h);
+	surface->width = w;
+	surface->height = h;
 
 	weston_view_configure(view, x, y, w, h);