eo: temporary prevent segfault.

In some case, detected during eo test suite, the vtable does fail to
be fully assigned, but it is still being assigned as the new vtable.
Of course when later destroying it, it has already been freed. Leading
to a double free.

src/lib/eo/eo.c

@@ -1642,6 +1642,8 @@ efl_object_override(Eo *eo_id, const Efl_Object_Ops *ops)
           {
              // FIXME: Maybe leaking some chain stuff from copy above?
              ERR("Failed to override functions for %p", eo_id);
+             if (obj->opt->vtable == vtable)
+               EO_OPTIONAL_COW_SET(obj, vtable, NULL);
              free(vtable);
              goto err;
           }