Fix "too many results returned" error after distro upgrades
    
    It turns out we had an error path that caused gnome-software to error
    out when the offline update results file listed more than 500 packages,
    which is an easy limit to cross for distro upgrades.
    
    This backports an upstream patch that fixes this.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1496489