CheckBox: AutoSize = true causes control to not be visible

[tig]

This unit test should be added to CheckBoxTests.cs:

		[Fact, AutoInitShutdown]
		public void AutoSize_StaysVisible ()
		{

			var checkBox = new CheckBox () {
				X = 1,
				Y = Pos.Center (),
				Text = "Check this out 你"
			};
			var win = new Window () {
				Width = Dim.Fill (),
				Height = Dim.Fill (),
				Title = "Test Demo 你"
			};
			win.Add (checkBox);
			Application.Top.Add (win);

			Assert.False (checkBox.IsInitialized);

			var runstate = Application.Begin (Application.Top);
			((FakeDriver)Application.Driver).SetBufferSize (30, 5);

			Assert.True (checkBox.IsInitialized);
			Assert.Equal ("Check this out 你", checkBox.Text);

			var expected = @"
┌ Test Demo 你 ──────────────┐
│                            │
│ ╴ Check this out 你        │
│                            │
└────────────────────────────┘
";

			// Positive test
			var pos = GraphViewTests.AssertDriverContentsWithFrameAre (expected, output);

			// Negative test
			checkBox.AutoSize = true;
			bool first = false;
			Application.RunMainLoopIteration (ref runstate, true, ref first);

			GraphViewTests.AssertDriverContentsWithFrameAre (expected, output);
		}

Output as of now:

 Terminal.Gui.Views.CheckboxTests.AutoSize_StaysVisible
   Source: CheckboxTests.cs line 72
   Duration: 106 ms

  Message: 
    Assert.Equal() Failure
                                      ↓ (pos 63)
    Expected: ···                │\n│ ╴ Check this out 你        │\n│            ···
    Actual:   ···                │\n│                            │\n│           ···
                                      ↑ (pos 63)

  Stack Trace: 
    GraphViewTests.AssertDriverContentsWithFrameAre(String expectedLook, ITestOutputHelper output) line 208
    CheckboxTests.AutoSize_StaysVisible() line 112

  Standard Output: 
    Expected:
    ┌ Test Demo 你 ──────────────┐
    │                            │
    │ ╴ Check this out 你        │
    │                            │
    └────────────────────────────┘
    But Was:
    ┌ Test Demo 你 ──────────────┐
    │                            │
    │ ╴ Check this out 你        │
    │                            │
    └────────────────────────────┘
    Expected:
    ┌ Test Demo 你 ──────────────┐
    │                            │
    │ ╴ Check this out 你        │
    │                            │
    └────────────────────────────┘
    But Was:
    ┌ Test Demo 你 ──────────────┐
    │                            │
    │                            │
    │                            │
    └────────────────────────────┘