Merge PR#288 from philipWendland:upstream-ecc-fix

add the possibility to store public ECC keys encoded according to SPKI
EC pubkey storing: Check if params are available before copying.
pkcs15-lib.c / sc_pkcs15init_store_public_key may be called with keyargs->key.u.ec.params.value == NULL. In this case, allocating and copying the parameters will fail. Add a check to prevent this.