efl_canvas_layout_part_external: implement missing functions

Summary:
this just prints a error, manipulating the content here is not
permitted. As it is created by edje externals, which are owned by edje.

ref T5719
Depends on D7757

Reviewers: cedric, zmike, segfaultxavi

Reviewed By: zmike

Subscribers: q66, #reviewers, #committers

Tags: #efl

Maniphest Tasks: T5719

Differential Revision: https://phab.enlightenment.org/D7759

src/lib/edje/edje_part_external.c

@@ -22,4 +22,18 @@ _efl_canvas_layout_part_external_efl_content_content_get(const Eo *obj, void *_p
    return _edje_object_part_external_object_get(pd->ed, pd->part);
 }
 
+EOLIAN static Eina_Bool
+_efl_canvas_layout_part_external_efl_content_content_set(Eo *obj EINA_UNUSED, void *pd EINA_UNUSED, Efl_Gfx_Entity *content EINA_UNUSED)
+{
+   ERR("Setting of content is not permitted on this part");
+   return EINA_FALSE;
+}
+
+EOLIAN static Efl_Gfx_Entity*
+_efl_canvas_layout_part_external_efl_content_content_unset(Eo *obj EINA_UNUSED, void *pd EINA_UNUSED)
+{
+   ERR("Unsetting of content is not permitted on this part");
+   return NULL;
+}
+
 #include "efl_canvas_layout_part_external.eo.c"

src/lib/edje/efl_canvas_layout_part_external.eo

@@ -25,6 +25,7 @@ class @beta Efl.Canvas.Layout_Part_External extends Efl.Canvas.Layout_Part imple
    ]]
    data: null;
    implements {
-      Efl.Content.content { get; }
+      Efl.Content.content { get; set; }
+      Efl.Content.content_unset;
    }
 }