Add extension point to change EmptyLineSelectionWidth.

Author: Alexander Shutov

ICSharpCode.AvalonEdit/Rendering/BackgroundGeometryBuilder.cs

@@ -244,7 +244,7 @@ static IEnumerable<Rect> ProcessTextLines(TextView textView, VisualLine visualLi
 						continue;
 					if (segmentStartVCInLine == visualStartCol && i > 0 && segmentStartVC < segmentStartVCInLine && visualLine.TextLines[i - 1].TrailingWhitespaceLength == 0)
 						continue;
-					yield return new Rect(pos, y, 1, line.Height);
+					yield return new Rect(pos, y, textView.EmptyLineSelectionWidth, line.Height);
 				} else {
 					Rect lastRect = Rect.Empty;
 					if (segmentStartVCInLine <= visualEndCol) {

ICSharpCode.AvalonEdit/Rendering/TextView.cs

@@ -2104,5 +2104,13 @@ public int HighlightedLine {
 			get { return this.currentLineHighlighRenderer.Line; }
 			set { this.currentLineHighlighRenderer.Line = value; }
 		}
+
+		/// <summary>
+		/// Empty line selection width.
+		/// </summary>
+		public virtual double EmptyLineSelectionWidth
+		{
+			get { return 1; }
+		}
 	}
 }