btrfs-progs: fsck: finish transaction commit if repair error out

btrfs-progs: fsck: finish transaction commit if repair error out

If btrfsck fail to repair, we hit something like following:

Check tree block failed, want=29442048, have=0
Check tree block failed, want=29442048, have=0
Check tree block failed, want=29442048, have=0
Check tree block failed, want=29442048, have=0
Check tree block failed, want=29442048, have=0
read block failed check_tree_block
found 98304 bytes used err is 1
total csum bytes: 0
total tree bytes: 0
total fs tree bytes: 0
total extent tree bytes: 0
btree space waste bytes: 0
file data blocks allocated: 0
referenced 0
Btrfs v3.14.2-rc2-63-g3944f15
btrfs: transaction.h:38: btrfs_start_transaction: Assertion `!(root->commit_root)' failed.
Aborted (core dumped)

This is because under repair mode, we will start a transaction, and if we error out,
we don't finish this transaction. So in close_ctree(), it will try
to start and commit transaction which causes the above segmentation.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>