Evas textblock: fix cached markup's stringshare refs

The last fix 34020ed131 was missing a
stringshare_del for the NOP case of markup_set. It led to a
constantly increasing ref count of the cached markup.

@fix

src/lib/evas/canvas/evas_object_textblock.c

@@ -6853,6 +6853,7 @@ _evas_textblock_text_markup_set(Eo *eo_obj EINA_UNUSED, Evas_Textblock_Data *o,
         text = eina_stringshare_add(text);
         if (text == o->markup_text)
           {
+             eina_stringshare_del(text);
              /* Text is the same, do nothing. */
              return;
           }