[fix] Transfer: fix a undefined JS error

doc/changelog/changelog_v1.4.13.md

+# Version v1.4.13
+
+## All platforms
+
+- [enh] Upgrade some JS libs: bower 1.8.8, angular 1.5.11, chart.js 2.9.3
+- [fix] Build: Better dependencies management: update the `bower.json`, and remove libs from `www/js/vendor` 
+  and `www/lib/ionic/angular`
+- [fix] Cesium+: fix charts X axis labels
+
+## Android
+
+
+## Desktop
+

www/js/controllers/transfer-controllers.js

@@ -257,7 +257,7 @@ function TransferModalController($scope, $q, $translate, $timeout, $filter, $foc
     }
 
     $scope.form.$valid = valid;
-    $scope.form.amount.$invalid = !valid;
+    if ($scope.form.amount) $scope.form.amount.$invalid = !valid;
 
     if (!valid || !$scope.formData.all || !amount) {
       $scope.formData.restAmount = undefined;