LU-16194 lod: define negative extent offset as invalid

LU-16194 lod: define negative extent offset as invalid

If lu_extent.e_start/e_end is negative after converting to s64,
regard it as invalid data except -1 (EOF).

Signed-off-by: Lei Feng <flei@whamcloud.com>
Change-Id: I79276a5185f339e9de48fe87c4da39052c7974e1
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48684
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>