Fixing an inutile exception.

Terminal.Gui/Views/ComboBox.cs

@@ -197,7 +197,7 @@ namespace Terminal.Gui {
 		}
 
 		///<inheritdoc/>
-		public override bool OnEnter ()
+		public override bool OnEnter (View view)
 		{
 			if (!search.HasFocus) {
 				this.SetFocus (search);

Terminal.Gui/Views/ListView.cs

@@ -206,7 +206,7 @@ namespace Terminal.Gui {
 		public int SelectedItem {
 			get => selected;
 			set {
-				if (source == null)
+				if (source == null || source.Count == 0)
 					return;
 				if (selected < 0 || selected >= source.Count)
 					throw new ArgumentException ("value");