If we can't fetch an icon, use something more sensible

Since we were previously throwing exceptions if the file couldn't be
found, the default we were using didn't really matter. Now we'll try
something (slightly) more sane.

src/VisualStudio/Core/Def/Implementation/Preview/FileChange.cs

@@ -227,7 +227,9 @@ internal override void GetDisplayData(VSTREEDISPLAYDATA[] pData)
                 }
             }
 
-            pData[0].Image = pData[0].SelectedImage = (ushort)StandardGlyphGroup.GlyphLibrary;
+            pData[0].Image = pData[0].SelectedImage
+                = document.Project.Language == LanguageNames.CSharp ? (ushort)StandardGlyphGroup.GlyphCSharpFile :
+                                                                      (ushort)StandardGlyphGroup.GlyphGroupClass;
         }
 
         private static IHierarchicalDifferenceCollection ComputeDiffSpans(ITextDifferencingService diffService, TextDocument left, TextDocument right, CancellationToken cancellationToken)