Add NewGRFClass helper method for whether any UI classes available

src/newgrf_class.h

@@ -57,6 +57,7 @@ public:
 	static void Assign(Tspec *spec);
 	static uint GetClassCount();
 	static uint GetUIClassCount();
+	static bool HasUIClass();
 	static Tid GetUIClass(uint index);
 	static NewGRFClass *Get(Tid cls_id);
 

src/newgrf_class_func.h

@@ -131,6 +131,18 @@ DEFINE_NEWGRF_CLASS_METHOD(uint)::GetUIClassCount()
 	return cnt;
 }
 
+/**
+ * Get whether at least one class is available to the user.
+ * @return Whether at least one class is available to the user.
+ */
+DEFINE_NEWGRF_CLASS_METHOD(bool)::HasUIClass()
+{
+	for (uint i = 0; i < Tmax && classes[i].global_id != 0; i++) {
+		if (classes[i].GetUISpecCount() > 0) return true;
+	}
+	return false;
+}
+
 /**
  * Get the nth-class with user available specs.
  * @param index UI index of a class.
@@ -223,6 +235,7 @@ DEFINE_NEWGRF_CLASS_METHOD(const Tspec *)::GetByGrf(uint32 grfid, byte local_id,
 	template NewGRFClass<Tspec, Tid, Tmax> *name::Get(Tid cls_id); \
 	template uint name::GetClassCount(); \
 	template uint name::GetUIClassCount(); \
+	template bool name::HasUIClass(); \
 	template Tid name::GetUIClass(uint index); \
 	template const Tspec *name::GetSpec(uint index) const; \
 	template int name::GetUIFromIndex(int index) const; \

src/object_gui.cpp

@@ -755,7 +755,7 @@ static WindowDesc _build_object_desc(
 Window *ShowBuildObjectPicker()
 {
 	/* Don't show the place object button when there are no objects to place. */
-	if (ObjectClass::GetUIClassCount() > 0) {
+	if (ObjectClass::HasUIClass()) {
 		return AllocateWindowDescFront<BuildObjectWindow>(&_build_object_desc, 0);
 	}
 	return nullptr;

src/terraform_gui.cpp

@@ -221,7 +221,7 @@ struct TerraformToolbarWindow : Window {
 	{
 		/* Don't show the place object button when there are no objects to place. */
 		NWidgetStacked *show_object = this->GetWidget<NWidgetStacked>(WID_TT_SHOW_PLACE_OBJECT);
-		show_object->SetDisplayedPlane(ObjectClass::GetUIClassCount() != 0 ? 0 : SZSP_NONE);
+		show_object->SetDisplayedPlane(ObjectClass::HasUIClass() ? 0 : SZSP_NONE);
 		SetWidgetDisabledState(WID_TT_BUY_LAND, _settings_game.construction.purchase_land_permitted == 0);
 	}