Fix build with OPENSSL_NO_ENGINE

Signed-off-by: Fredrik Fornwall <fredrik@fornwall.net>

lib/net_mosq.c

@@ -103,7 +103,9 @@ void net__cleanup(void)
 	#if OPENSSL_VERSION_NUMBER < 0x10100000L
 		ERR_remove_state(0);
 	#endif
-	ENGINE_cleanup();
+	#ifndef OPENSSL_NO_ENGINE
+		ENGINE_cleanup();
+	#endif
 	CONF_modules_unload(1);
 	ERR_free_strings();
 	EVP_cleanup();