EX-7601 ofd: don't read for writes past eof

EX-7601 ofd: don't read for writes past eof

There's no data past EOF, so there's no need to do
read-modify-writes when the entire write is past the chunk
at EOF.  So in that case, don't read up data and don't
attempt decompression.

There's no explicit test for this, but this shows up
immediately in the random-offset copy tests, because they
seek and write various sizes to offsets past current EOF.

We also need this functionality for reads, because in some
cases the client will do reads past EOF (this is unusual,
but can still happen sometimes).  This is added in a
separate patch because it requires some code reorganization.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Ia2b598165d5645c5a44c3d58bea69c7e42f10e41
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53425
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>