Clear signal speed restriction at game shutdown

src/misc.cpp

@@ -118,6 +118,7 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 
 	FreeSignalPrograms();
 	FreeSignalDependencies();
+
 	ClearAllSignalSpeedRestrictions();
 
 	ClearZoningCaches();

src/openttd.cpp

@@ -439,6 +439,9 @@ static void ShutdownGame()
 	FreeSignalPrograms();
 	FreeSignalDependencies();
 
+	extern void ClearAllSignalSpeedRestrictions();
+	ClearAllSignalSpeedRestrictions();
+
 	ClearZoningCaches();
 	ClearOrderDestinationRefcountMap();