Better null checking

One test was crashing (even on rerun), so maybe this will fix

src/Controls/src/Core/Compatibility/Handlers/ListView/iOS/CellTableViewCell.cs

@@ -33,28 +33,28 @@ public Cell Cell
 			get => _cell?.GetTargetOrDefault();
 			set
 			{
-				if (_cell is null)
-				{
-					_cell = new(value);
-				}
-				else
+				if (_cell is not null)
 				{
 					if (_cell.TryGetTarget(out var cell) && cell == value)
 						return;
 
-					if (cell != null)
+					if (cell is not null)
 					{
 						cell.PropertyChanged -= HandlePropertyChanged;
 						BeginInvokeOnMainThread(cell.SendDisappearing);
 					}
-					_cell = new(value);
 				}
 
-				if (value != null)
+				if (value is not null)
 				{
+					_cell = new(value);
 					value.PropertyChanged += HandlePropertyChanged;
 					BeginInvokeOnMainThread(value.SendAppearing);
 				}
+				else
+				{
+					_cell = null;
+				}
 			}
 		}
 

src/Controls/src/Core/Compatibility/Handlers/ListView/iOS/ViewCellRenderer.cs

@@ -60,11 +60,7 @@ public ViewCell ViewCell
 				get => _viewCell?.GetTargetOrDefault();
 				set
 				{
-					if (_viewCell is null)
-					{
-						_viewCell = new(value);
-					}
-					else
+					if (_viewCell is not null)
 					{
 						if (_viewCell.TryGetTarget(out var viewCell) && viewCell == value)
 							return;
@@ -192,15 +188,16 @@ void UpdateCell(ViewCell cell)
 					oldCell.View.MeasureInvalidated -= OnMeasureInvalidated;
 				}
 
-				_viewCell = new(cell);
-
 				if (cell is null)
 				{
+					_viewCell = null;
 					_rendererRef = null;
 					ContentView.ClearSubviews();
 					return;
 				}
 
+				_viewCell = new(cell);
+
 				cell.PropertyChanged += ViewCellPropertyChanged;
 				BeginInvokeOnMainThread(cell.SendAppearing);