EX-8996 ofd: handle 'missing object' reads

EX-8996 ofd: handle 'missing object' reads

When the read code (eg, mdt_preprw_read) finds there is no
object, it will return a read with 0 pages, but not fail the
read.  The assert for local and remote pages needs to
recognize this case.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Idc6ff70f71abc100f750a63eca73a754a56f6435
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53807
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>