Fix k5crypto NSS iov processing bug

In k5_nss_gen_stream_iov(), don't stop processing the iov array if we
run across a zero-length iov.

(cherry picked from commit 08fafff29a11e61036021196aaae8c303d1a5662)

https://github.com/krb5/krb5/commit/4682cfb7696231ddf4a34f9d048233012266b657
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 4682cfb7696231ddf4a34f9d048233012266b657
Branch: krb5-1.14
 src/lib/crypto/nss/enc_provider/enc_gen.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)