Guard setCurrentViewingUser against undefined from find()

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/stores/acctMgmt.ts

@@ -74,6 +74,7 @@ export const useAcctMgmtStore = defineStore('acctMgmtStore', {
      */
     setCurrentViewingUser(username: string) {
       const userFind = this.allUserAccountList.find(user => user.username === username);
+      if (!userFind) return;
       this.currentViewingUser = userFind;
     },
     /**