ike-sa-manager: Unlock mutex if allocating SPI fails to avoid lock contention

Fixes: 5d91d8c46937 ("Check rng return value when generating SPIs in ike_sa_manager_t")
Signed-off-by: Thomas Egerer <thomas.egerer@secunet.com>

src/libcharon/sa/ike_sa_manager.c

@@ -1151,6 +1151,7 @@ static status_t check_and_put_init_hash(private_ike_sa_manager_t *this,
 	spi = get_spi(this);
 	if (!spi)
 	{
+		mutex->unlock(mutex);
 		return FAILED;
 	}