Merge pull request #147 from perosb/getExtFix

Dont throw exeption if querystring is null

Former-commit-id: 04f373b26853975be3cb3fe2bb9a2a399834ac9c
Former-commit-id: c9d985754818f52593604adcd882516076ec1758
Former-commit-id: 36b8a53dbcefe75dfa810f839754a678eb1ade34

src/ImageProcessor.Web/Helpers/ImageHelpers.cs

@@ -78,7 +78,12 @@ namespace ImageProcessor.Web.Helpers
             {
                 // Test against the path minus the querystring so any other
                 // processors don't interere.
-                string trimmed = fullPath.Replace(queryString, string.Empty);
+                string trimmed = fullPath;
+                if (queryString != null)
+                {
+                    trimmed = trimmed.Replace(queryString, string.Empty);
+                }
+                
                 match = FormatRegex.Match(trimmed);
             }