Fix JS error when randomize checkbox is missing

static/js/upload.js

@@ -42,7 +42,10 @@ Dropzone.options.dropzone = {
         file.uploadElement.setAttribute("style", 'background-image: -webkit-linear-gradient(left, #F2F4F7 ' + p + '%, #E2E2E2 ' + p + '%); background-image: -moz-linear-gradient(left, #F2F4F7 ' + p + '%, #E2E2E2 ' + p + '%); background-image: -ms-linear-gradient(left, #F2F4F7 ' + p + '%, #E2E2E2 ' + p + '%); background-image: -o-linear-gradient(left, #F2F4F7 ' + p + '%, #E2E2E2 ' + p + '%); background-image: linear-gradient(left, #F2F4F7 ' + p + '%, #E2E2E2 ' + p + '%)');
     },
     sending: function(file, xhr, formData) {
-		formData.append("randomize", document.getElementById("randomize").checked);
+        var randomize = document.getElementById("randomize");
+        if(typeof randomize != "undefined") {
+            formData.append("randomize", randomize.checked);
+        }
         formData.append("expires", document.getElementById("expires").value);
     },
     success: function(file, resp) {