WP_oEmbed::fetch() doesn't give any results if the provider doesn't support JSON
|Reported by:||nbachiyski||Owned by:||Viper007Bond|
A request is made for JSON format and if we get an error we give up on that provider.
According to the oEmbed specification a provider should return 501 Not Implemented if it doesn't support the format. We should respect that and try the next format, instead of immediately failing.