speed.c: fix segfault with unrecognized algorithms

When an unrecognized algorithm is given on command line together with
-async_jobs, speed_main will jump to clean-up and run
ASYNC_cleanup_thread without calling ASYNC_init_thread first.

Example:
openssl speed -async_jobs 4 ras2048

Signed-off-by: Cristian Stoica <cristian.stoica@nxp.com>

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1084)