REST API: Capability check for editing a single term should use the singular form.

As an extra level of sanity checking, the term ID should be cast as an int in `map_meta_cap()`.

Props johnbillion, nacin, dd32, pento.
See #35614.
Fixes #39012.



git-svn-id: https://develop.svn.wordpress.org/trunk@39464 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/capabilities.php

@@ -427,7 +427,7 @@ function map_meta_cap( $cap, $user_id ) {
 	case 'edit_term':
 	case 'delete_term':
 	case 'assign_term':
-		$term_id = $args[0];
+		$term_id = (int) $args[0];
 		$term = get_term( $term_id );
 		if ( ! $term || is_wp_error( $term ) ) {
 			$caps[] = 'do_not_allow';