[BugFix] do_menu skinlist_draw dangling reference

skinlist_draw stores a pointer to the list supplied
if this pointer goes out of scope we may try to access it

toggle_theme has a path to handle this but if you move to a a item with the
theme enabled it doesn't release the pointer
later the pointer will be referenced long after it has gone out of scope

limiting this to do_menu() if other areas are problematic the previous
version of this patch applies it system-wide

Change-Id: I57c73d789856cb1a660fb704f02ca55c8978a4d0

apps/menu.c

@@ -769,7 +769,10 @@ int do_menu(const struct menu_item_ex *start_menu, int *start_selected,
     }
 
     FOR_NB_SCREENS(i)
+    {
         viewportmanager_theme_undo(i, false);
+        skinlist_set_cfg(i, NULL); /* Bugfix dangling reference in skin_draw() */
+    }
 #ifdef HAVE_TOUCHSCREEN
     /* This is needed because this function runs the settings menu and we do
      * not want to switch back to the old mode if the user intentionally went