PurchaseWidget: Handle when it fails to load options

Fixes APP-AY

assets/langs/en.yaml

@@ -174,6 +174,9 @@ widgets:
       other: "{} Notes link to this Note"
   SortingOrderSelector:
     title: Sorting Criteria
+  PurchaseButton:
+    text: Purchase for {price}
+    fail: Failed to Load
 
 rootFolder: Root Folder
 ignoredFiles:

lib/widgets/purchase_slider.dart

@@ -59,6 +59,10 @@ class ShapePainter extends CustomPainter {
 
   @override
   void paint(Canvas canvas, Size size) {
+    if (values.isEmpty) {
+      return;
+    }
+
     var paint = Paint()
       ..color = color
       ..strokeWidth = 2

lib/widgets/purchase_widget.dart

@@ -22,12 +22,20 @@ class PurchaseButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    var price = product != null ? product.price : "Dev Mode";
+    String text;
+    if (product != null) {
+      text = tr("widgets.PurchaseButton.text", namedArgs: {
+        'price': product.price,
+      });
+      if (subscription) {
+        text += '/ $timePeriod';
+      }
+    } else {
+      text = tr("widgets.PurchaseButton.fail");
+    }
 
     return RaisedButton(
-      child: subscription
-          ? Text('Purchase for $price / $timePeriod')
-          : Text('Purchase for $price'),
+      child: Text(text),
       color: Theme.of(context).primaryColor,
       padding: const EdgeInsets.fromLTRB(32.0, 16.0, 32.0, 16.0),
       onPressed: product != null ? () => _initPurchase(context) : null,