Adjust AdditionalHorizontalScrollAmount to a more reasonable amount.

This avoids the large whitespace to the right of the text when AvalonEdit is used in size-to-content mode.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/TextView.cs

@@ -811,7 +811,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		/// Additonal amount that allows horizontal scrolling past the end of the longest line.
 		/// This is necessary to ensure the caret always is visible, even when it is at the end of the longest line.
 		/// </summary>
-		const double AdditionalHorizontalScrollAmount = 30;
+		const double AdditionalHorizontalScrollAmount = 3;
 		
 		Size lastAvailableSize;
 		bool inMeasure;