Fix use-after-free bug in prepare_push_reply()

Fix use-after-free bug in prepare_push_reply()

This was introduced by commit dfd3513e, which changes the push_cipher
memory allocation from the options gc to a temporary gc.  For the
ciphername in the options structure, which has to be available longer,
change this back to using the options gc.

Apologies for not spotting this during patch review.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1476905060-29896-1-git-send-email-steffan@karger.me>
URL: http://www.mail-archive.com/search?l=mid&q=1476905060-29896-1-git-send-email-steffan@karger.me
Signed-off-by: Gert Doering <gert@greenie.muc.de>