ContentOffset fixed.

Terminal.Gui/Views/ScrollBarView.cs

@@ -126,11 +126,11 @@ namespace Terminal.Gui {
 			set {
 				var co = -Math.Abs (value);
 				if (contentOffset != co) {
-					if (CanScroll (contentOffset - co, out int max, vertical)) {
+					if (CanScroll (value + contentOffset, out int max, vertical) || max > 0) {
 						if (max == contentOffset - co) {
 							contentOffset = co;
 						} else {
-							contentOffset = co + max;
+							contentOffset = -max;
 						}
 					}
 					Position = Math.Max (0, -contentOffset);

UICatalog/Scenarios/Editor.cs

@@ -94,7 +94,7 @@ namespace UICatalog {
 			_textView.DrawContent += (e) => {
 				_vertical.Size = _textView.Lines - 1;
 				_vertical.ContentOffset = _textView.TopRow;
-				horizontal.Size = _textView.Maxlength;
+				horizontal.Size = _textView.Maxlength + 1;
 				horizontal.ContentOffset = _textView.LeftColumn;
 				_vertical.ColorScheme = horizontal.ColorScheme = _textView.ColorScheme;
 				if (_vertical.ShowScrollIndicator) {