AJAX paging breaks badly when json_encode can't encode

[westi]

If json_encode can't encode a response for some reason you get no feedback at all except for a blank list.

This seems most likely to trigger with invalid UTF8 sequences in spam comments.

With non-ajax paging you at least get all the comments displayed even if you do get a lot of ??? for the bad chars

Example Error seen:

[15-Dec-2010 14:18:38] Warning: json_encode() [<a href='function.json-encode'>function.json-encode</a>]: Invalid UTF-8 sequence in argument in /home/wpdev/public_html/wp-admin/includes/class-wp-list-table.php on line 839 [

This is one reason I proposed a standard way of doing Ajax in #14618: it handles erroneous or syntactically invalid responses in a consistent manner.

In this case we could pass the href attribute value to the error handler and have it set location.href to load the requested page when Ajax paging fails.

We can strip invalid characters with wp_check_invalid_utf8(). Patch included.

Related: #11175