PR# 12904 Hidden diagram is not updated when relations change

If diagram is hidden during recompilation, it is not updated when relations between classes change.

1. Create and compile a system with the following set of classes:
	class A end
	class B end
	class C inherit
		B
	end
2. Open "Diagram" tab, ensure that inheritance links are shown and put there classes A, B, C. Observe that there is a link from C to B.
3. Press a button to view the diagram in UML format. Ensure that all these classes are shown and the inheritance links are correct.
4. Switch back to BON format.
5. Select some other tab, for example, to "Feature Relations", so that the "Diagram" tab becomes hidden.
6. Change class C as follows:
	class C inherit
		A
	end
7. Recompile the system.
8. Select "Diagram" tab.
9. Observe that the inheritance links are not updated.
10. Recompile one more time more.
11. Observe that the inheritance links are now updated.
12. Switch to UML view of the diagram.
13. Observe that the inheritance links are not updated.

Fixed in rev#69355. Thanks.