DocumentUtilitites.GetTextSource: unwrap existing ITextSource instead of creating a double adapter

src/Main/Base/Project/Src/Editor/AvalonEdit/AvalonEditDocumentAdapter.cs

@@ -20,7 +20,7 @@ namespace ICSharpCode.SharpDevelop.Editor.AvalonEdit
 	/// </summary>
 	public class AvalonEditDocumentAdapter : IDocument
 	{
-		readonly TextDocument document;
+		internal readonly TextDocument document;
 		readonly IServiceProvider parentServiceProvider;
 		
 		/// <summary>

src/Main/Base/Project/Src/Editor/AvalonEdit/AvalonEditTextSourceAdapter.cs

@@ -12,7 +12,7 @@ namespace ICSharpCode.SharpDevelop.Editor.AvalonEdit
 {
 	public class AvalonEditTextSourceAdapter : ITextBuffer
 	{
-		ITextSource textSource;
+		internal readonly ITextSource textSource;
 		
 		public AvalonEditTextSourceAdapter(ITextSource textSource)
 		{

src/Main/Base/Project/Src/Editor/DocumentUtilitites.cs

@@ -8,10 +8,10 @@
 using System;
 using System.Diagnostics;
 using System.Windows.Documents;
-
 using ICSharpCode.AvalonEdit;
 using ICSharpCode.AvalonEdit.Document;
 using ICSharpCode.AvalonEdit.Utils;
+using ICSharpCode.SharpDevelop.Editor.AvalonEdit;
 
 namespace ICSharpCode.SharpDevelop.Editor
 {
@@ -178,6 +178,15 @@ namespace ICSharpCode.SharpDevelop.Editor
 		{
 			if (textBuffer == null)
 				throw new ArgumentNullException("textBuffer");
+			
+			var textSourceAdapter = textBuffer as AvalonEditTextSourceAdapter;
+			if (textSourceAdapter != null)
+				return textSourceAdapter.textSource;
+			
+			var documentAdapter = textBuffer as AvalonEditDocumentAdapter;
+			if (documentAdapter != null)
+				return documentAdapter.document;
+			
 			return new TextBufferTextSource(textBuffer);
 		}