Only retransmit on Finished if frag_off == 0.

If the peer fragments Finished into multiple pieces, there is no need to
retransmit multiple times.

Change-Id: Ibf708ad079e1633afd420ff1c9be88a80020cba9
Reviewed-on: https://boringssl-review.googlesource.com/3762
Reviewed-by: Adam Langley <agl@google.com>
2 files changed