LU-13324 llite: page delete race

LU-13324 llite: page delete race

Page could be raced by truncate during its deletion by
another thread, check vmpage mapping before accessing it.

Lustre-change: https://review.whamcloud.com/37793
Lustre-commit: 8ccaed513006f0582578ff42c9917b5aa76f2f4b

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I3172f5ffd3928926b16ab6fd7362b05da0c7cfd5
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/38111
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>