Fix programmable signal programs not being cleared in InitializeGame.

This could leave dangling signal programs in subsequent games
which can cause crashes during saving.

src/misc.cpp

@@ -28,6 +28,7 @@
 #include "core/pool_type.hpp"
 #include "game/game.hpp"
 #include "linkgraph/linkgraphschedule.h"
+#include "programmable_signals.h"
 
 #include "safeguards.h"
 
@@ -74,6 +75,9 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 	LinkGraphSchedule::Clear();
 	PoolBase::Clean(PT_NORMAL);
 
+	FreeSignalPrograms();
+	FreeSignalDependencies();
+
 	ResetPersistentNewGRFData();
 
 	InitializeSound();