Fix test18566 to have the correct expectation

Before the test was allowing invalid encoding in PKCS#1 data, but this
is an exploitable condition in certain cases. See for instance
https://www.imperialviolet.org/2014/09/26/pkcs1.html

Since BoringSSL has the change to disallow this problem, we are
switching this to assert that the signature did not verify.

Bug: 21209498
Bug: 5038554
Bug: http://code.google.com/p/android/issues/detail?id=18566
Change-Id: Ie040f644a4588c6801e5557e2f9a3bcdedfd30ac
1 file changed