LU-15431 llite: skip fast reads if layout is invalid

LU-15431 llite: skip fast reads if layout is invalid

don't let fast reads from the pagecache if the layout
is not valid.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ie4357a184faf9a5d0e33804270d3cb0cb7e67bb7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/46282
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>