agent: Compute correct MPI length header for protected ECC keys.
* agent/cvt-openpgp.c (apply_protection): Strip leading zeroes from opaque MPIs to comply with the OpenPGP spec.
This patch is the protected private key counterpart to commit ab17f7b.
Thanks to andy_s for describing the problem.
- GnuPG-bug-id: T1853
- Signed-off-by: Werner Koch <wk@gnupg.org>