coredump: cescape invalid json data before logging
    
    In both cases, the json string is short, so we can print it, which is useful
    for diagnosing invalid data in packages. But we need escape non-printable
    characters.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=2152685
    
    I went over the rest of the codebase, and it seems that other calls to
    json_parse() don't have this problem.
    
    (cherry picked from commit c5966ab5bf43b4fb45998760beaffa6c7f9e8a9e)