Fixing the condition that considers a list empty

Author: wberube

src/app_config.c

@@ -44,7 +44,7 @@ int save_app_config(void) {
 
     fprintf(file, "system:\n");
     fprintf(file, "  web_port: %d\n", app_config.web_port);
-    if (app_config.web_whitelist) {
+    if (!EMPTY(*app_config.web_whitelist)) {
         fprintf(file, "  web_whitelist: ");
         for (int i = 0; app_config.web_whitelist[i] && *app_config.web_whitelist[i]; i++) {
             fprintf(file, "    - %s\n", app_config.web_whitelist[i]);