Fix automatic handling of failures during image upload

[azaozz]

Follow up from #17474.

After testing this in WP 5.3 beta and RC it became apparent that some servers may be configured to set different error codes on PHP fatal errors, for example 508 or 504. To catch all of them it would be best to look at all HTTP 5xx errors while post-processing images in #17858.

This is already implemented in the media modal and the old uploader code, see https://core.trac.wordpress.org/ticket/48379 and https://core.trac.wordpress.org/changeset/46566.

[azaozz]

The only change needed would be from
( response.status === 500 || response.status === 502 )
to
( response.status >= 500 && response.status < 600 )

[youknowriad]

Duplicate of #18081

[azaozz]

Ah, sorry, didn't see #18081 was just created for the same thing :)