Add missing terminating NULL to speed_options table.

This would cause memory corruption in opt_init() because it relies on the
terminating NULL.

RT#3842

Reviewed-by: Rich Salz <rsalz@openssl.org>

apps/speed.c

@@ -374,6 +374,7 @@ OPTIONS speed_options[] = {
 #ifndef OPENSSL_NO_ENGINE
     {"engine", OPT_ENGINE, 's', "Use engine, possibly a hardware device"},
 #endif
+    {NULL},
 };
 
 #define D_MD2           0