ntfs: fix variable dereferenced before check ni and attr in ntfs_attrlist_entry_add()

ntfs: fix variable dereferenced before check ni and attr in ntfs_attrlist_entry_add()

Smatch warnings:

ntfs_attrlist_entry_add() warn: variable dereferenced before check 'ni'
ntfs_attrlist_entry_add() warn: variable dereferenced before check 'attr'

Moves the ntfs_debug() call after the NULL pointer checks to ensure safe
access to the structure members.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>