hwclock: add iso-8601 overflow check

hwclock: add iso-8601 overflow check

hwclock wasn't testing for strtimeval_iso() truncation:

/sbin/hwclock --utc --noadjfile --predict --date '7982 years'; echo $?
9999-09-25 19:33:01.000000-0400
0

/sbin/hwclock --utc --noadjfile --predict --date '7983 years'; echo $?
10000-09-25 19:33:10.000000-
0

Patched:
./hwclock --utc --noadjfile --predict --date '7982 years'; echo $?
9999-09-25 19:22:15.000000-0400
0

./hwclock --utc --noadjfile --predict --date '7983 years'; echo $?
hwclock: iso-8601 format truncated
1

Signed-off-by: J William Piggott <elseifthen@gmx.com>