Check if it's a CSGO demo

Must be verified, edited from my smartphone :p

Author: Calak

DemoInfo/DemoParser.cs

@@ -501,6 +501,9 @@ public void ParseHeader()
 			if (header.Filestamp != "HL2DEMO")
 				throw new InvalidDataException("Invalid File-Type - expecting HL2DEMO");
 
+			if (header.GameDirectory != "csgo")
+				throw new InvalidDataException("Invalid Demo-Game");
+
 			if (header.Protocol != 4)
 				throw new InvalidDataException("Invalid Demo-Protocol");