Catch existing url in yourls db

[danito]

When submitting an existing url to yourls, response = .

{  "status":"fail",
    "code":"error:url",
    "url":{
              "keyword":"a",
              "url":"http:\/\/0",
              "title":"400 Bad Request",
              "date":"2015-06-16 14:06:15",
              "ip":"2a00:d0c0:200:0:b9:1a:9c2b:109",
              "clicks":"0"
             },
      "message":"http:\/\/0 already exists in database",
      "title":"400 Bad Request",
      "shorturl":"http:\/\/nixis.me\/a",
      "statusCode":200
}

[danito]

fixed