f2fs: handle unallocated section and zone on pinned/atgc

If we have large section/zone, unallocated segment makes them corrupted.

E.g.,

  - Pinned file:       -1 119304647 119304647
  - ATGC   data:       -1 119304647 119304647

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>