dmesg: avoid mess at the end of dmesg output

dmesg: avoid mess at the end of dmesg output

Since util-linux commit a7ee94f2204011f26232ed3133514bf6e0d4a62c,
dmesg incorrectly calculates number of bytes that are remaining in the
buffer in get_next_record(). This could, under specific circumstances,
cause printing mess at the end of dmesg output:

> dmesg | tail
[ 1191.478725] Adding 285488k swap on /root/swapfile.  Priority:-2 extents:15 across:1186612k
[ 1205.588331] Adding 285488k swap on /root/swapfile.  Priority:-2 extents:15 across:1186612k
\xffffffba\xffffffba

Reported-by: Glenn Doig <doiggl@velocitynet.com.au>
Addresses: https://bugzilla.novell.com/show_bug.cgi?id=710417

Signed-off-by: Petr Uzel <petr.uzel@suse.cz>