fix: null-check the correct variable

Author: goaaats

src/XIVLauncher.Common/Game/Launcher.cs

@@ -42,10 +42,7 @@ public Launcher(ISteam? steam, IUniqueIdCache uniqueIdCache, ISettings settings,
         this.uniqueIdCache = uniqueIdCache;
         this.settings = settings;
 
-        if (this.frontierUrlTemplate == null)
-            throw new Exception("Frontier URL template is null, this is now required");
-
-        this.frontierUrlTemplate = frontierUrl;
+        this.frontierUrlTemplate = frontierUrl ?? throw new Exception("Frontier URL template is null, this is now required");
 
         ServicePointManager.Expect100Continue = false;