Fixing 302 redirect for URLs with no extensions

[anukasha-mo]

Summary of my changes:

• Updated wp_audio_shortcode() and wp_video_shortcode() to only return a plain link when the URL does not have any extension.
• Made the type attribute on tags conditional i.e. when the MIME type cannot be determined (redirect URLs), the type attribute is omitted entirely rather than rendered as type="", which allows the browser to probe the MIME type itself (apparently that's the same thing YouTube and Vimeo embeds do).

Trac ticket: https://core.trac.wordpress.org/ticket/31689

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