* scd/app-sc-hsm.c: Re-indendet some parts and set some vars to NULL
after xfree for improbed robustness.
(read_ef_prkd): Replace serial operator by blocks for better
readability.
(apply_PKCS_padding): Rewrite for easier auditing.
(strip_PKCS15_padding): Ditto.  Add stricter check on SRCLEN.