Wrong "Is already open" message when diving into subcircuit

[flandreas]

Scenario to reproduce the bug:

• Open a circuit containing a "Full Adder"
• ALT-doubleclick on "Full Adder" to open it in secondary view
• META-doubleclick on "Half Adder" in secondary circuit to dive into "Half Adder"
• Re-surface from "Half Adder"
• ALT-doubleclick on the same "Half Adder"

=> Antares says "Is already open", which is wrong.

[flandreas]

Occurs only occasionally if the technical ID's of opened subcircuits happen to be the same. Fixed.