LU-10267 llog: fix EOF handling in llog_client_next_block()

LU-10267 llog: fix EOF handling in llog_client_next_block()

In llog_client_next_block() update *cur_idx and *cur_offset in the
special case that the handler has returned -EIO after reaching the end
of the log without finding the desired record. This fixes client side
EOF detection in llog_process_thread().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: If30ebec065ddd38fb7b06c3e16f96bb3cd76fa1b
Reviewed-on: https://review.whamcloud.com/30313
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>