fsck.f2fs: fix corrupted nat entry [0]
fsck.f2fs: fix corrupted nat entry [0]

The first nat entry must be null. If it is corrupted, we set its bit in
nat_area_bitmap, without increasing valid_nat_entry_cnt, fsck_verify will
nullify it at last.

Reported-by: Cheng Yinchao <4cec2d1b48c8844920d9327cd28ee03d9110192f@huawei.com>
Signed-off-by: Sheng Yong <ce77ec10379c6f281208b7b41f03fd701be51d81@huawei.com>
Signed-off-by: Jaegeuk Kim <71255387a32c360dfbe6dfb7aaeb123bf1dc8cb6@kernel.org>

TeamExodus/external_f2fs-tools,TeamExodus/external_f2fs-tools