add Sync.AssertUnsynced. use it in OrderGenerator.set

OpenRA.Game/Sync.cs

@@ -132,19 +132,31 @@ namespace OpenRA
 
 		public static void CheckSyncUnchanged( World world, Action fn )
 		{
-			int sync = world.SyncHash();
-			fn();
-			if( sync != world.SyncHash() )
-				throw new InvalidOperationException( "Desync in DispatchMouseInput" );
+			CheckSyncUnchanged( world, () => { fn(); return true; } );
 		}
 
+		static bool inUnsyncedCode = false;
+
 		public static T CheckSyncUnchanged<T>( World world, Func<T> fn )
 		{
 			int sync = world.SyncHash();
-			var ret = fn();
-			if( sync != world.SyncHash() )
-				throw new InvalidOperationException( "Desync in DispatchMouseInput" );
-			return ret;
+			inUnsyncedCode = true;
+			try
+			{
+				return fn();
+			}
+			finally
+			{
+				inUnsyncedCode = false;
+				if( sync != world.SyncHash() )
+					throw new InvalidOperationException( "Desync in DispatchMouseInput" );
+			}
+		}
+
+		public static void AssertUnsynced( string message )
+		{
+			if( !inUnsyncedCode )
+				throw new InvalidOperationException( message );
 		}
 	}
 }