2-page form, displaying on 2nd page, want to skip empty fields

Greetings,
I'm trying to do exactly what this post title suggests.
Here's my test page: http://goo.gl/8zV8c
Page 1 of my form will have 125 products to choose from, each with a quantity field.
Page 2, the html field should display only values that the user has entered on Page 1 along with the product title and price.
I've messed around with the foreach loop that builds the html content as outlined in the third code snippet here:
http://www.gravityhelp.com/documentation/page/Gform_pre_render

//this is a complex fieldset (name, adress, etc.) - get individual field info
					foreach($field["inputs"] as $input){
						//get name of individual field, replace period with underscore when pulling from post
						$input_name = "input_" . str_replace(".","_",$input["id"]);
						$value = rgpost($input_name);
						$html_content .= "<li>" . $value . " value: " . $input_name . "</li>";
					}

But I don't know how to check to see if the user has entered a quantity for a specific product field or not.
Any help is greatly appreciated.