When yield a.k.a "generator" iterator is used we need to return all
data using "yield", before returning from the function.
Because of that only encryption tests were run for AES-CBC, other modes
were affected as well.
Add one more loop to the iterator "next" routine to fix that.
This unveiled a problem in the GCM AEAD parser logic, which didn't
correctly handle tests cases with empty plaintext, i.e. AAD only.
Include the fix in this patch as it's a rather trivial one.
Obtained from: Semihalf
Differential Revision: https://reviews.freebsd.org/D36861
fdbd0ba75d