Feature: Allow <resource> to have only one of source and destination

This allows <resource> (former <alias>) to have only one of the
attribues source and destination. In that case other parameters
will be applied to the client but uri is not mapped.

See #2097

src/cfgfile.c

@@ -1692,15 +1692,16 @@ static void _parse_paths(xmlDocPtr doc, xmlNodePtr node,
             alias = malloc(sizeof(aliases));
             alias->next = NULL;
             alias->source = (char *)xmlGetProp(node, XMLSTR("source"));
-            if(alias->source == NULL) {
-                free(alias);
-                continue;
-            }
             alias->destination = (char *)xmlGetProp(node, XMLSTR("destination"));
             if (!alias->destination)
                 alias->destination = (char *)xmlGetProp(node, XMLSTR("dest"));
-            if(alias->destination == NULL) {
+
+            if (!alias->source && alias->destination) {
+                alias->source = alias->destination;
+                alias->destination = NULL;
+            } else if(!alias->source && !alias->destination) {
                 xmlFree(alias->source);
+                xmlFree(alias->destination);
                 free(alias);
                 continue;
             }

src/connection.c

@@ -1269,7 +1269,8 @@ static int _handle_aliases(client_t *client, char **uri) {
            (alias->port == -1 || alias->port == serverport) &&
            (alias->bind_address == NULL || (serverhost != NULL && strcmp(alias->bind_address, serverhost) == 0)) &&
            (alias->vhost == NULL || (vhost != NULL && strcmp(alias->vhost, vhost) == 0)) ) {
-            new_uri = strdup(alias->destination);
+            if (alias->destination)
+                new_uri = strdup(alias->destination);
             if (alias->omode != OMODE_DEFAULT)
                 client->mode = alias->omode;
             ICECAST_LOG_DEBUG("alias has made %s into %s", *uri, new_uri);