These FIXMEs were already addressed in 2013. All functions check for
qgroup existence:

* btrfs_add_qgroup_relation
* btrfs_ioctl_qgroup_create
* btrfs_limit_qgroup
* btrfs_del_qgroup_relation
Signed-off-by: NDaichou <tommy0705c@gmail.com>
[ enhance and reformat changelog ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>