title: fast-csv is throwing exception : column header mismatch expected
body: <p>I am trying to validate data using fast-csv.
  My code looks like </p>
  
  <pre><code>var fileName = req.files.uploadcsv.path;
  var fs = require("fs");
  
  var stream = fs.createReadStream(fileName);
  
  var csv = require("fast-csv");
  
  csv
      .fromStream(stream, {
          headers: true
      })
      .validate(function(data) {
              if (data.age &gt; 18)
                  return false;
              else
                  return true;
  
          }
  
      }
  </code></pre>
  
  <p>It works fine for every file I uploaded but if I uploaded file with extra data, it says 
  Error: Unexpected Error: column header mismatch expected: 5 columns got: 6
  Actually the file has 5 headers but data set it contains have 6 records.
  I want to catch this error so that I can point users to error.</p>
  
  <p>Please suggest.</p>