Fix #10335: Set initial scrollbar count for object GUI. (#10336)

This previously happened when the window was resized by itself which was fixed by #10196. Explicitly set the count instead.

src/object_gui.cpp

@@ -119,6 +119,7 @@ public:
 
 		NWidgetMatrix *matrix = this->GetWidget<NWidgetMatrix>(WID_BO_SELECT_MATRIX);
 		matrix->SetScrollbar(this->GetScrollbar(WID_BO_SELECT_SCROLL));
+		matrix->SetCount(ObjectClass::Get(_selected_object_class)->GetUISpecCount());
 
 		this->GetWidget<NWidgetMatrix>(WID_BO_OBJECT_MATRIX)->SetCount(4);