LU-5933 fiemap: set FIEMAP_EXTENT_LAST correctly

LU-5933 fiemap: set FIEMAP_EXTENT_LAST correctly

When we've collected enough extents as user requested, we'd check one
further to decide whether we've reached the last extent of the file.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: Ic4c4710adf98552626d87d54c893ba9fa18ef7b8
Reviewed-on: http://review.whamcloud.com/12781
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>