Fix uninitialized crypto pattern

Apps built against an older API don't have the recently
added pattern field in MediaCodec.CryptoInfo which causes
the crypto pattern fields to be uninitialized.  This change
ensures the pattern is initialized in all cases.

bug: 27477422
Change-Id: I5796bf5fbca93dba5bf9a2b74c1c6638b9e90f65