Fix for exception throw when validating URLs (#7701)

src/Umbraco.Core/StringExtensions.cs

@@ -79,6 +79,21 @@ namespace Umbraco.Core
 
         }
 
+        /// <summary>
+        /// Determines the extension of the path or URL
+        /// </summary>
+        /// <param name="file"></param>
+        /// <returns>Extension of the file</returns>
+        public static string GetFileExtension(this string file)
+        {
+            //Find any characters between the last . and the start of a query string or the end of the string
+            const string pattern = @"(?<extension>\.[^\.\?]+)(\?.*|$)";
+            var match = Regex.Match(file, pattern);
+            return match.Success
+                ? match.Groups["extension"].Value
+                : string.Empty;
+        }
+
         /// <summary>
         /// Based on the input string, this will detect if the string is a JS path or a JS snippet.
         /// If a path cannot be determined, then it is assumed to be a snippet the original text is returned