f2fs: fix to requery extent which cross boundary of inquiry

dd if=/dev/zero of=file bs=4k count=5
xfs_io file -c "fiemap -v 2 16384"
file:
   EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
     0: [0..31]:         139272..139303      32 0x1000
     1: [32..39]:        139304..139311       8 0x1001
xfs_io file -c "fiemap -v 0 16384"
file:
   EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
     0: [0..31]:         139272..139303      32 0x1000
xfs_io file -c "fiemap -v 0 16385"
file:
   EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
     0: [0..39]:         139272..139311      40 0x1001

There are two problems:
- continuous extent is split to two
- FIEMAP_EXTENT_LAST is missing in last extent

The root cause is: if upper boundary of inquiry crosses extent,
f2fs_map_blocks() will truncate length of returned extent to
F2FS_BYTES_TO_BLK(len), and also, it will stop to query latter
extent or hole to make sure current extent is last or not.

In order to fix this issue, once we found an extent locates
in the end of inquiry range by f2fs_map_blocks(), we need to
expand inquiry range to requiry.

Cc: stable@vger.kernel.org
Fixes: 7f63eb77 ("f2fs: report unwritten area in f2fs_fiemap")
Reported-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>