Fix error message on starting game due to missing global variable.

This was SVN commit r14110.

binaries/data/mods/public/gui/session/session.js

@@ -3,6 +3,8 @@ var g_IsNetworked = false;
 
 // Is this user in control of game settings (i.e. is a network server, or offline player)
 var g_IsController;
+// Match ID for tracking
+var g_MatchID
 
 // Cache the basic player data (name, civ, color)
 var g_Players = [];