Fix potential NullPointerException in FileState.

If you accessed `file.Url` without being saved yet, you would crash. Very bad.

Author: richardjrossiii

Parse/Internal/File/State/FileState.cs

@@ -13,7 +13,7 @@ internal class FileState {
     public Uri SecureUrl {
       get {
         Uri uri = Url;
-        if (uri.Host == ParseFileSecureDomain) {
+        if (uri != null && uri.Host == ParseFileSecureDomain) {
           return new UriBuilder(uri) {
             Scheme = ParseFileSecureScheme,
             Port = -1, // This makes URIBuilder assign the default port for the URL scheme.