ssh: handle error from prepareKeyChange.

Fixes #18850.

Change-Id: Id3ae89233f9e95ec3238462bf2ecda3e0c515f88
Reviewed-on: https://go-review.googlesource.com/36051
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
1 file changed