JS autosave_update_slug() doesn't check if return is -1

[nacin]

If check_ajax_referer() fails, it'll die with -1. In autosave_update_slug(), we don't account for that, which results in a goofy -1 in the HTML.

See the example here: ​http://cl.ly/0Q341X010Z0c2H3s1R1I. Probably the most common reason for the check to fail would be if the user has since logged out, as you can see in the bottom right corner of the screenshot. I often see this when I discover tabs that I opened days before.

[azaozz]

Patch looks good, just one question: wouldn't it be better to leave the current slug unchanged (whatever it may be) instead of removing it?

[nacin]

Sure, that could work. It'd always come back when the user is logged in. I'm indifferent.

[azaozz]

(In [17565]) Handle error response in autosave_update_slug(), props nacin, fixes #16975