btrfs-progs: convert: Fix a bug leads to discontinuous extents

btrfs-progs: convert: Fix a bug leads to discontinuous extents

Btrfs_record_file_extent() will split extents using max extent size(128M).
It works well for real file extents, but not that well for large
hole extent, as hole doesn't have extent size limit.

In that case, it will only insert one 128M hole, and skip the rest,
leading to discontinuous extent error for converted btrfs.

Fix it by not splitting hole extents.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>