btrfs-progs: fix btrfs-image old_restore fsck failure

btrfs-progs: fix btrfs-image old_restore fsck failure

Steps to reproduce:
	# mkfs.btrfs -f <dev1>
	# btrfs-image <dev1> <image_file>
	# btrfs-image -r -o <image_file> <dev2>
	# btrfs check <dev2>

btrfs check output:
	: read block failed check_tree_block
	: Couldn't read tree root
	: Couldn't open file system

The btrfs-image should not mess with the chunk tree under the old_restore way.

The new restore way was introduced by:
	commit d6f7e3da0dae7b60cb7565f8a47c3b9045c52d1d
	Btrfs-progs: make btrfs-image restore with a valid chunk tree V2
	...
And the following commit enhanced the new restore on the valid chunk tree
building stuff:
	commit ef2a8889ef813ba77061f6a92f4954d047a78932
	Btrfs-progs: make image restore with the original device offsets
	...

But the second commit should not effect the old_restore way since the
old_restore way doesn't try to build a valid chunk tree at all.

Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>