ecore_x: Avoid crash on NULL

This happens in E with software compositing, since E's commit
5702f0975e890f07cfb. E should be fixed shortly but segv is not
acceptable. Without segv E is still massively broken so it's
not like the bug would be hidden (large black areas in windows,
after switch vdesks with enough windows).

src/lib/ecore_x/ecore_x_image.c

@@ -502,6 +502,9 @@ ecore_x_image_to_argb_convert(void *src,
    };
    int mode = 0;
 
+   EINA_SAFETY_ON_NULL_RETURN_VAL(src, EINA_FALSE);
+   EINA_SAFETY_ON_NULL_RETURN_VAL(dst, EINA_FALSE);
+
    sbpp *= 8;
 
    n = vis->map_entries;