Bug#841028: CUPS hangs with 100% CPU usage using web interface

[John Scott <jscott@posteo.net>]

It might be different from what everyone else is dealing with, but having
just enabled Kerberos in the CUPS interface after getting tickets, I tried
modifying a printer in the web interface that was not yet configured to use
it. This appears to cause CUPS to get in a loop calling cupsdDoSelect()
forever:
#0  cupsdDoSelect (timeout=1) at select.c:400
        nfds = <optimized out>
        fdptr = <optimized out>
        pfd = <optimized out>
        count = <optimized out>
#1  0x0000558ad494d283 in main (argc=<optimized out>, argv=<optimized out>) at main.c:847
        i = 2
        opt = <optimized out>
        close_all = <optimized out>
        disconnect = <optimized out>
        fg = <optimized out>
        run_as_child = <optimized out>
        print_profile = <optimized out>
        fds = 2
        con = <optimized out>
        job = <optimized out>
        lis = <optimized out>
        current_time = <optimized out>
        activity = <optimized out>
        senddoc_time = 1603730037
        expire_time = 1603730038
        report_time = 0
        event_time = 1603729690
        timeout = 1
        limit = {rlim_cur = 524288, rlim_max = 524288}
        action = {__sigaction_handler = {sa_handler = 0x558ad49644b0 <sigterm_handler>, sa_sigaction = 0x558ad49644b0 <sigterm_handler>}, 
          sa_mask = {__val = {81920, 0 <repeats 15 times>}}, sa_flags = 0, sa_restorer = 0x0}
        netif_time = 1603730018
        service_idle_exit = 0

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