When adding a Custom Link and leaving the "Link Text" field empty, WordPress used to set a default fallback text: "Menu Item".
The changes in [36379] broke this behavior making the fallback text: ` (Pending)`, with a leading space.
Pending major refactoring of the Menus page (which is going to use a block-based user interface) this change just restores the original behavior by adding the fallback text to the related AJAX response.
Props christophherr, Fencer04, thakkarhardik, backermann1978, audrasjb.
Fixes#38415.
git-svn-id: https://develop.svn.wordpress.org/trunk@45727 602fd350-edb4-49c9-b593-d223f7449a82