Fix null check around adding Container.Child to logical children.
Fix null check around adding Container.Child to logical children.


SuperJMN/Avalonia,grokys/Perspex,jkoritzinsky/Avalonia,MrDaedra/Avalonia,wieslawsoltes/Perspex,SuperJMN/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,akrisiun/Perspex,AvaloniaUI/Avalonia,Perspex/Perspex,AvaloniaUI/Avalonia,Perspex/Perspex,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,MrDaedra/Avalonia,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,grokys/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,jkoritzinsky/Perspex,SuperJMN/Avalonia,AvaloniaUI/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,jazzay/Perspex,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia