Fixed lookup of relative paths for build errors.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@5649 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Base/Project/Src/Project/MSBuildEngine/MSBuildEngine.cs

@@ -400,8 +400,8 @@ namespace ICSharpCode.SharpDevelop.Project
 					file = "";
 				} else if (FileUtility.IsValidPath(file)) {
 					bool isShortFileName = file == Path.GetFileNameWithoutExtension(file);
-					if (projectFile != null) {
-						file = Path.Combine(Path.GetDirectoryName(projectFile), file);
+					if (engine.ProjectFileName != null) {
+						file = Path.Combine(Path.GetDirectoryName(engine.ProjectFileName), file);
 					}
 					if (isShortFileName && !File.Exists(file)) {
 						file = "";