f2fs: check data eof after partial truncation on compressed cluster

f2fs: check data eof after partial truncation on compressed cluster

This is a regression testcase, it is added to check below case
and its variants:
- write 16k data into compressed file (data will be compressed)
- truncate file to 12k (truncate partial data in compressed cluster)
- truncate file to 20k
- verify data in range of [12k, 16k] to see whether data is all zero
or not

Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>