LU-632 utils: fix problems of llog_reader

LU-632 utils: fix problems of llog_reader

When the input file of llog_reader is invalid, it is easy to
crash or loop infinitely. This patch fixes these problems.

Signed-off-by: Li Xi <pkuelelixi@gmail.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Change-Id: Ifd6bbc5e857f6910bb4103d85742ba33a843d080
Reviewed-on: http://review.whamcloud.com/10764
Tested-by: Jenkins
Reviewed-by: Artem Blagodarenko <artem.blagodarenko@seagate.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>