TinyMCE, inline link: when searching, do not empty the URL input field when using the arrow keys to highlight items.

Props afercia.
See #33301.

git-svn-id: https://develop.svn.wordpress.org/trunk@36974 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/js/tinymce/plugins/wplink/plugin.js

@@ -348,6 +348,7 @@
 						},
 						focus: function( event, ui ) {
 							$input.attr( 'aria-activedescendant', 'mce-wp-autocomplete-' + ui.item.ID );
+							event.preventDefault();
 						},
 						select: function( event, ui ) {
 							$input.val( ui.item.permalink );

src/wp-includes/js/wplink.js

@@ -76,6 +76,7 @@ var wpLink;
 				},
 				focus: function( event, ui ) {
 					$input.attr( 'aria-activedescendant', 'mce-wp-autocomplete-' + ui.item.ID );
+					event.preventDefault();
 				},
 				select: function( event, ui ) {
 					$input.val( ui.item.permalink );