lscpu: fix floating point exception

lscpu: fix floating point exception

As the title tells this change indeed fixes floating point exception, but
post processing as value overwrite feels a wrong.  Possibly something in
input is making cpu set count to go wrong, but I could not get my head
around what could it be.  Anyway avoiding division by zero seems better than
crashing so lets do this atleast for now.

Caused-by: e5f721132ec8b8c933a396d8dcb3efcb67854f13
Addresses: https://github.com/karelzak/util-linux/issues/788
Reported-by: Lars Wendler <polynomial-c@gentoo.org>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>