Tidy up image resizing example

samples/misc/NodeServicesExamples/Node/resizeImage.js

@@ -1,7 +1,8 @@
 var sharp = require('sharp');
 
 module.exports = function(result, physicalPath, mimeType, maxWidth, maxHeight) {
+    // Invoke the 'sharp' NPM module, and have it pipe the resulting image data back to .NET
     sharp(physicalPath)
-        .resize(maxWidth > 0 ? maxWidth : null, maxHeight > 0 ? maxHeight : null)
+        .resize(maxWidth || null, maxHeight || null)
         .pipe(result.stream);
 }