staging: erofs: keep corrupted fs from crashing kernel in erofs_readdir()

staging: erofs: keep corrupted fs from crashing kernel in erofs_readdir()

After commit 6dc4a64410c5, kernel cannot be crashed in the namei
path. However, corrupted nameoff can do harm in the process of
readdir for scenerios without dm-verity as well. Fix it now.

Fixes: a8dc4aab0a6a ("staging: erofs: add directory operations")
Cc: <stable@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>