Zoning: Cache expensive zoning overlay values

src/misc.cpp

@@ -33,6 +33,7 @@
 #include "viewport_func.h"
 #include "bridge_signal_map.h"
 #include "command_func.h"
+#include "zoning.h"
 
 #include "safeguards.h"
 
@@ -90,6 +91,8 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 	FreeSignalPrograms();
 	FreeSignalDependencies();
 
+	ClearZoningCaches();
+
 	ResetPersistentNewGRFData();
 
 	InitializeSound();