[Lazarus] IDE form visibility bug on Linux

[AlexeyT]

Ubuntu latest, gnome desktop

- open IDE (two windows opened: main and messages, some test proj loaded)
- click "minimize" icon on main wnd
- restore wnd again: click Ubuntu sidebar lazarus icon - previews appear 
in small rects - choose main wnd
- main wnd restored
- click "Open" toolbar button on main wnd
==> IDE window and Open dialog hide
or
==> all ok

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Regards,
Alexey