Fixed SD2-845:Null reference exception when attempting to show tooltip for XSLT output

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@1501 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Base/Project/Src/Services/RefactoringService/NRefactoryRefactoringProvider.cs

@@ -22,13 +22,12 @@ namespace ICSharpCode.SharpDevelop.Refactoring
 		public override bool IsEnabledForFile(string fileName)
 		{
 			string extension = Path.GetExtension(fileName);
-			if (extension.Equals(".cs", StringComparison.InvariantCultureIgnoreCase))
-				return true;
-			else if (extension.Equals(".vb", StringComparison.InvariantCultureIgnoreCase))
-				return true;
-			else
+			if (extension == null) {
 				return false;
 			}
+			return extension.Equals(".cs", StringComparison.InvariantCultureIgnoreCase) ||
+				   extension.Equals(".vb", StringComparison.InvariantCultureIgnoreCase);
+		}
 		
 		#region FindUnusedUsingDeclarations
 		protected class PossibleTypeReference