Fix WebUI crash due to missing tags from config

Tags can be missing from config but set inside .fastresume. May happen due to corrupted/deleted config.
Closes #11906.
PR #16711.

src/webui/www/private/scripts/client.js

@@ -374,6 +374,12 @@ window.addEvent('load', function() {
         let added = false;
         for (let i = 0; i < tags.length; ++i) {
             const tagHash = genHash(tags[i].trim());
+            if (!tagList[tagHash]) { // This should not happen
+                tagList[tagHash] = {
+                    name: tags,
+                    torrents: []
+                };
+            }
             if (!Object.contains(tagList[tagHash].torrents, torrent['hash'])) {
                 added = true;
                 tagList[tagHash].torrents.push(torrent['hash']);