Extra caption button displayed on macOS due to missing platform check

[ChiahongHong]

In the refactoring made in ef4b639, the condition for HasRightCaptionButton doesn't check properly. As a result, an extra caption button is displayed on macOS.

sourcegit/src/Views/Launcher.axaml.cs

Lines 32 to 35 in ef4b639

	public bool HasRightCaptionButton
	{
	get => OperatingSystem.IsWindows() || !Native.OS.UseSystemWindowFrame;
	}

[love-linger]

Fixed.