LU-14143 lov: fix SEEK_HOLE calcs at component end

LU-14143 lov: fix SEEK_HOLE calcs at component end

If data ends exactly at component end then LOV assumed that
is not yet hole in file and the next component will take care.
Meanwhile there can be no next component initialized yet if file
ends exactly at component boundary, so no hole offset is returned
but error

Patch fixes that issue. If component reports hole offset at
component end then it is saved to be used as result when no
other components report valid hole offset.

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I8bffd8b76546b560a3d34034701eea4963f41593
Reviewed-on: https://review.whamcloud.com/40713
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>