database: Restart flatten algorithm from the top when a network was dropped

We used to simply take the first element from the stack after we have
split a network. That is wrong because it is not passing through any
filters and no further subnet checks. It could have therefore been
that the tree was not entirely flat.
Reported-by: Arne Fitzenreiter <arne_f@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

src/database.c

@@ -1380,11 +1380,10 @@ static int __loc_database_enumerator_next_network_flattened(
 	loc_network_list_unref(subnets);
 	loc_network_list_unref(excluded);
 
-	// Replace network with the first one from the stack
+	// Drop the network and restart the whole process again to pick the next network
 	loc_network_unref(*network);
-	*network = loc_network_list_pop_first(enumerator->stack);
 
-	return 0;
+	return __loc_database_enumerator_next_network_flattened(enumerator, network);
 }
 
 LOC_EXPORT int loc_database_enumerator_next_network(