LU-12586 lov: one more fix to write_intent end for trunc

LU-12586 lov: one more fix to write_intent end for trunc

This patch fixes another case where the truncate write intent
extent is set incorrectly.  This may cause errors when truncating
PFL files to exactly the boundary between two extents.

Fixes: c32c7401426d ("LU-12586 lov: Correct write_intent end for trunc")
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I40f14a48c53bfd1e6442e4414ee30f9eb159fc02
Reviewed-on: https://review.whamcloud.com/38412
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>