Don't improperly cast IDs when fetching post, user, or term objects.

Blindly casting passed IDs to integers can generate false positives
when the ID is cast to `1`.

Props deeptiboddapati.
Fixes #37738.
Built from https://develop.svn.wordpress.org/trunk@38381


git-svn-id: http://core.svn.wordpress.org/trunk@38322 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-comment.php

@@ -191,11 +191,12 @@ final class WP_Comment {
 	public static function get_instance( $id ) {
 		global $wpdb;
 
-		$comment_id = (int) $id;
-		if ( ! $comment_id ) {
+		if ( ! is_numeric( $id ) || $id != floor( $id ) || ! $id ) {
 			return false;
 		}
 
+		$comment_id = (int) $id;
+
 		$_comment = wp_cache_get( $comment_id, 'comment' );
 
 		if ( ! $_comment ) {