Always show the OpenSSL error queue after failure.

Any failed OpenSSL function may have pushed errors onto the error queue.
Thus, after any failed OpenSSL function it needs to be cleared otherwise
it may leave errors on the queue for future operations.

Signed-off-by: Adam Langley <agl@chromium.org>
(EB: made error_msg_openssl() call do_error_msg())
Signed-off-by: Eric Biggers <ebiggers@google.com>