fix #496: ContextActionBulbControl: it should always be displayed inside the editor's view port bounds

Author: siegfriedpammer

src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/AvalonEditEditorUIService.cs

@@ -67,8 +67,10 @@ public IOverlayUIElement CreateOverlayUIElement(UIElement element)
 		/// <inheritdoc />
 		public Point GetScreenPosition(int line, int column)
 		{
-			var positionInPixels = textView.PointToScreen(
-				textView.GetVisualPosition(new TextViewPosition(line, column), VisualYPosition.LineBottom) - textView.ScrollOffset);
+			var visualPosition = textView.GetVisualPosition(
+				new TextViewPosition(line, column), VisualYPosition.LineBottom) - textView.ScrollOffset;
+			var positionInPixels = textView.PointToScreen(new Point(visualPosition.X.CoerceValue(0, textView.ActualWidth),
+			                                                        visualPosition.Y.CoerceValue(0, textView.ActualHeight)));
 			return positionInPixels.TransformFromDevice(textView);
 		}
 

src/Main/Base/Project/Editor/IEditorUIService.cs

@@ -37,6 +37,8 @@ public interface IEditorUIService
 
 		/// <summary>
 		/// Gets the absolute screen position of given position in the document.
+		/// If the position is outside of the currently visible portion of the document,
+		/// the value is forced into the viewport bounds.
 		/// </summary>
 		Point GetScreenPosition(int line, int column);