btrfs-progs: tests: Fix fuzz-test for bko-161821.raw.txt

btrfs-progs: tests: Fix fuzz-test for bko-161821.raw.txt

Fuzzed image bko-161821.raw causes btrfs check to get segmentation fault.

The function check_owner_ref attempts to access a non-exist quota tree
when dealing with extent_item [4198400 4096] in the corrupted filesystem.

The function btrfs_new_fs_info always allocates memory for
fs_info->quota_root regardless of whether quota_tree exists or not.
Additionally, the function btrfs_read_fs_root will directly return
fs_info->quota_root if location->objectid == BTRFS_QUOTA_TREE_OBJECTID.

This patch does the following things:
1. Do extra check and return ENOENT if quota tree does not exist in the
   function btrfs_read_fs_root.
2. Free useless fs_info->quota_root in the function btrfs_setup_all_roots
   to reduce confusion.
3. free_extent_buffer even if check_child_node failed in the function
   walk_down_tree.

Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>