evas-wayland-shm: Don't post updates to surface if no surface

evas-wayland-shm: Don't post updates to surface if no surface

In the event that an ecore_evas (using wayland_shm) gets hidden then
the corresponding wl_surface gets destroyed. If evas_norender is
called after that, the outbuf_redraws_clear function follows.
Outbuf_redraw_clear function ends up trying to post updates to the
wl_surface however if that wl_surface is gone, then we end up crashing.

This patch addresses that issue by checking for a valid wl_surface
inside the engine before trying to post updates to that wl_surface.

Signed-off-by: Chris Michael <cp.michael@samsung.com>