Properly initialize $totalAmounts

Otherwise getAllTotalAmounts() does not return an array if no totals
have been added. Same goes for $baseTotalAmounts

Author: schmengler

app/code/Magento/Quote/Model/Quote/Address/Total.php

@@ -13,12 +13,12 @@ class Total extends \Magento\Framework\DataObject
     /**
      * @var array
      */
-    protected $totalAmounts;
+    protected $totalAmounts = [];
 
     /**
      * @var array
      */
-    protected $baseTotalAmounts;
+    protected $baseTotalAmounts = [];
 
     /**
      * Serializer interface instance.