[Node page] Add link to node list per country/isp in node page

frontend/src/app/shared/graphs.utils.ts

@@ -92,6 +92,9 @@ export function detectWebGL() {
 }
 
 export function getFlagEmoji(countryCode) {
+  if (!countryCode) {
+    return '';
+  }
   const codePoints = countryCode
     .toUpperCase()
     .split('')