ntfs: Fix null pointer dereference

ntfs: Fix null pointer dereference

The variable ctx can be null and once confirmed to be null in its error
path goes to label err_out. Once there it can be immediately dereferenced
by the function ntfs_attr_put_search_ctx() which has no null pointer check.

Detected by Smatch:
fs/ntfs/ea.c:687 ntfs_new_attr_flags() error:
we previously assumed 'ctx' could be null (see line 577)

Add null pointer check before running  ntfs_attr_put_search_ctx() in
error path.

Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>