LU-9994 obdclass: fix llog_cat_id2handle() error handling

LU-9994 obdclass: fix llog_cat_id2handle() error handling

Patch for LU-9153 ("llog: consolidate common error checking") has
introduced a regression in llog_cat_id2handle() error handling
path by adding llog_cat_process_common() common routine additional
call in sequence and allowing it to return zero even when catalog
entry was invalid and it had cleared it instead to populate
llog_handle, thus causing an exception when handle was later
dereferenced in llog_process_thread().

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I50153b931e3c1567bfe9c15564ba29fabe3a2d4c
Reviewed-on: https://review.whamcloud.com/29370
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>