LU-15119 tgt: BUG at tgt_brw_read+0x16bf/0x1d80

LU-15119 tgt: BUG at tgt_brw_read+0x16bf/0x1d80

struct tgt_thread_big_cache {
  local = {{
      lnb_file_offset = 0,
      lnb_page_offset = 0,
      lnb_len = 0,
      lnb_rc = 0,
      lnb_page = 0xffffddee74fae100,
so npages_read becomes 0

Change-Id: Ie2201c9fc6f0350b1c6dcb480cff52f44d5413db
HPE-bug-id: LUS-10510
Signed-off-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-on: https://review.whamcloud.com/45273
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>