fs/ntfs3: Potential NULL dereference in hdr_find_split()

The "e" pointer is dereferenced before it has been checked for NULL.
Move the dereference after the NULL check to prevent an Oops.

Fixes: 82cae269 ("fs/ntfs3: Add initialization of super block")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Kari Argillander <kari.argillander@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>