add error checks and return nil

Author: mbvreddy

Foundation/NSURL.swift

@@ -417,6 +417,11 @@ public class NSURL : NSObject, NSSecureCoding, NSCopying {
     /* A string constant for the "file" URL scheme. If you are using this to compare to a URL's scheme to see if it is a file URL, you should instead use the NSURL fileURL property -- the fileURL property is much faster. */
     public var standardizedURL: NSURL? {
         let urlComponent = NSURLComponents(string: relativeString)
+
+        guard urlComponent != nil && urlComponent!.path != nil else {
+            return nil
+        }
+
         urlComponent!.path = _standardizedURLPath(urlComponent!.path!)
         return urlComponent?.URLRelativeToURL(baseURL)
     }