Handle interrupted AJAX calls gracefully

[roytanck]

Currently, if the AJAX call that Plugin Report does to retrieve a plugin's info fails completely, the process breaks. All following plugins are not processed, and thus no info is shown for them.

We should add at least a very basic callback for when this happens, that displays a row, probably with an error message. Following rows should be processed.

This is related to https://wordpress.org/support/topic/wordpress-6-7-1-compatible/ .