Nav Menu Saving: get_nav_menu_locations() can return false, code expects array

[Viper007Bond]

get_nav_menu_locations() can return false (it is right now with Twenty Thirteen) but /wp-admin/nav-menu.php tries to always treat it as an array:

​https://core.trac.wordpress.org/browser/trunk/wp-admin/nav-menus.php?rev=23441#L277

This throws a warning and breaks stuff.

ticket:23119:23119.4.diff​ would fix it, see ticket:23119:224.

In 23453:

Fix a warning on Menus screen if $menu_locations is false.
Fix menu selection after creating a first menu on new install.

props jkudish.
fixes #23508. see #23119.

I think get_nav_menu_locations() should always return an array, as the docs say. Let's try to also fix that?

Ensures that get_nav_menu_locations() always returns an array.

23508.3.diff​ works for me.

Not sure if we need the ! empty() check, is_array() seems enough (23508.2.diff​).

In 23550:

Ensure that get_nav_menu_locations() always returns an array. props JustinSainton for initial patch. fixes #23508.