LU-9857 lmv: dir page is released while in use

LU-9857 lmv: dir page is released while in use

When popping stripe dirent, if it reaches page end,
stripe_dirent_next() releases current page and then reads next one,
but current dirent is still in use, as will cause wrong values used,
and trigger assertion.

This patch changes to not read next page upon reaching end, but
leave it to next dirent read.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: I28865d5719dfe95c0efba2f5543661a07aca6bd2
Reviewed-on: https://review.whamcloud.com/32180
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>