Cocoa: regression since Lazarus 2.2, parented form cannot hide

• Lazarus Version: today's Git
• Operating System: macOS El Capitan
• CPU / Bitness: x64

Run the demo. tst-form-hide.zip

demo has top 3 buttons for 3 parented forms (form-0, form-1, form-2):

• button 'show 0' shows child form-0 and hides other 2 forms
• button 'show 1' shows child form-1 and hides other 2 forms
• etc

If you press all 3 buttons many times (0, 1, 2, 0, 1, 2, 0, 1, 2, etc) you see that showing green-child-forms appear wrong. One of forms will stuck and others won't show themselves correctly.

Bug is in the fixes_3_0 too!