elm_layout_text_set() should return EINA_FALSE when it fails to set a text.
In the past, elm_layout_text_set() is implemented in other widgets which inherit elm_layout.
And all of them return EINA_FALSE when there is no proper part for internal Edje object.
But, after applying efl_text_set() interface, elm_layout_text_set() always return EINA_TRUE if part name has no problem.
It breaks backward compatibility. So, we need to fix it.