Add comment about split usage in osu:// protocol link handling

osu.Game/OsuGame.cs

@@ -921,6 +921,9 @@ namespace osu.Game
             if (!url.StartsWith(OSU_PROTOCOL, StringComparison.Ordinal))
                 throw new ArgumentException("Invalid osu URL provided.", nameof(url));
 
+            // note that `StringSplitOptions.RemoveEmptyEntries` is not explicitly specified here
+            // in order to ensure that the protocol URL is valid (i.e. it has two slashes in the `osu://` part,
+            // causing the link content to be stored to the 2nd index rather than the 1st).
             string[] pieces = url.Split('/');
 
             switch (pieces[2])