Via Tender: Validate Youtube trailer link

Assigned to Tender discussion #700. As reported in Tender:

This one has the youtube id as expected:

http://api.themoviedb.org/3/movie/18692/trailers

{
"id": 18692,
"quicktime": [

],
"youtube": [
    {
        "name": "Trailer",
        "size": "Standard",
        "source": "_rTncah2ZgU"
    }
]
}

But this one contains a full link:

http://api.themoviedb.org/3/movie/841/trailers

{
"id": 841,
"quicktime": [

],
"youtube": [
    {
        "name": "Trailer",
        "size": "Standard",
        "source": "http://www.youtube.com/watch?v=KwPTIEWTYEI"
    }
]
}