Add catch for compressed H2 MCC maps

instead of waiting for it to fail at the tags header and muddying things, the compressed flag is now checked to simply tell the user that the map is compressed. #366

src/Blamite/Blam/SecondGen/Structures/SecondGenHeader.cs

@@ -1,5 +1,6 @@
 using Blamite.Serialization;
 using Blamite.IO;
+using System;
 
 namespace Blamite.Blam.SecondGen.Structures
 {
@@ -98,6 +99,13 @@ public StructureValueCollection Serialize()
 
 		private void Load(StructureValueCollection values, FileSegmenter segmenter)
 		{
+			if (values.HasInteger("flags"))
+			{
+				int flags = (int)values.GetInteger("flags");
+				if ((flags & 1) > 0)
+					throw new ArgumentException("Map claims to be compressed. Please decompress it using the Tools menu before trying to load it again.");
+			}
+
 			uint filesize = (uint)values.GetInteger("file size");
 
 			uint metaOffset = (uint)values.GetInteger("meta offset");