BUG/MEDIUM: fix risk of segfault with "show tls-keys"

The reference to the tls_keys_ref was not deleted from the
tlskeys_reference linked list.

When the SSL is malconfigured, it can lead to an access to freed memory
during a "show tls-keys" on the admin socked.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index fed5bd5..d9afd84 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -8807,6 +8807,7 @@
 			if(bind_conf->keys_ref) {
 				free(bind_conf->keys_ref->filename);
 				free(bind_conf->keys_ref->tlskeys);
+				LIST_DEL(&bind_conf->keys_ref->list);
 				free(bind_conf->keys_ref);
 			}
 #endif /* USE_OPENSSL */