ocfs2: validate i_refcount_loc when refcount flag is set

Add validation in ocfs2_validate_inode_block() to check that if an inode
has OCFS2_HAS_REFCOUNT_FL set, it must also have a valid i_refcount_loc.
A corrupted filesystem image can have this inconsistent state, which later
triggers a BUG_ON in ocfs2_remove_refcount_tree() when the inode is being
wiped during unlink.

Catch this corruption early during inode validation to fail gracefully
instead of crashing the kernel.

Link: https://lkml.kernel.org/r/20251212055826.20929-1-kartikey406@gmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Reported-by: syzbot+6d832e79d3efe1c46743@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6d832e79d3efe1c46743
Tested-by: syzbot+6d832e79d3efe1c46743@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/20251208084407.3021466-1-kartikey406@gmail.com/T/ [v1]
Link: https://lore.kernel.org/all/20251212045646.9988-1-kartikey406@gmail.com/T/ [v2]
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>