NativeCrypto: empty data content for PKCS7 container
NativeCrypto: empty data content for PKCS7 container

The EncapsulatedContentInfo must be present in the output, but OpenSSL
will fill in a zero-length OID if you don't call PKCS7_set_content on the
outer PKCS7 container. So we construct an empty PKCS7 data container and
set it as the content. This fixes the invalid PKCS7 output.

Bug: 18664989
Change-Id: I6f4cf785dd02ee40f1951d098fa987aa25d2421a

google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt