Btrfs-progs: fix btrfs-map-logical to only print extent mapping info

Btrfs-progs: fix btrfs-map-logical to only print extent mapping info

I have a valid btrfs image which contains,
...
        item 10 key (1103101952 BLOCK_GROUP_ITEM 1288372224) itemoff 15947 itemsize 24
                block group used 655360 chunk_objectid 256 flags DATA|RAID5
        item 11 key (1103364096 EXTENT_ITEM 131072) itemoff 15894 itemsize 53
                extent refs 1 gen 11 flags DATA
                extent data backref root 5 objectid 258 offset 0 count 1
        item 12 key (1103888384 EXTENT_ITEM 262144) itemoff 15841 itemsize 53
                extent refs 1 gen 15 flags DATA
                extent data backref root 1 objectid 256 offset 0 count 1
        item 13 key (1104281600 EXTENT_ITEM 262144) itemoff 15788 itemsize 53
                extent refs 1 gen 15 flags DATA
                extent data backref root 1 objectid 257 offset 0 count 1
...

The extent [1103364096, 131072) has length 131072, but if we run

"btrfs-map-logical -l 1103364096 -b $((65536 * 3)) /dev/sda"

it will return mapping info 's of  non-existing extents.

It's because it assumes that extents's are contiguous on logical address,
when it's not true, after one loop (cur_logical += cur_len) and mapping
the next extent, we can get an extent that is out of our search range and
we end up with a negative @real_len and printing all mapping infos till
the disk end.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>