Merge pull request #4577 from dbartol/extension-fix/work

Fix path transformer handling of extensionless files

Author: Dave Bartolomeo

csharp/extractor/Semmle.Extraction/PathTransformer.cs

@@ -44,7 +44,14 @@ private struct TransformedPath : ITransformedPath
 
             public string Value => value;
 
-            public string Extension => Path.GetExtension(value)?.Substring(1) ?? "";
+            public string Extension
+            {
+                get
+                {
+                    var extension = Path.GetExtension(value);
+                    return string.IsNullOrEmpty(extension) ? "" : extension.Substring(1);
+                }
+            }
 
             public string NameWithoutExtension => Path.GetFileNameWithoutExtension(value);