params and options parameters validation is missing

[chaitanya-mahamuni]

Please add validations same as "Stylesheet.prototype.apply" method inside method below.

node-libxslt/index.js

Line 183 in c51e287

Stylesheet.prototype.applyToFile = function(sourcePath, params, options, callback) {

This method throws an error "TypeError: callback is not a function" if called only with 2 params as below:

// documentPath : some inaccessible invalid path
stylesheet.applyToFile(documentPath, function(error, result) {
    if( !err ) {
        // handle success
    } else {
        // handle error
    }
});

But above code works well with accessible valid value "documentPath".