Fix crash when no mailbox usage present

src/views/email.js

@@ -394,7 +394,10 @@ angular.module('Application').controller('EmailController', ['$scope', '$locatio
                     Client.getMailUsage($scope.domain.domain, function (error, usage) {
                         if (error) return callback(error);
 
-                        $scope.mailboxes.mailboxes.forEach(function (m) { m.usage = usage[m.name + '@' + m.domain].size || 0; });
+                        $scope.mailboxes.mailboxes.forEach(function (m) {
+                            var u = usage[m.name + '@' + m.domain]; // this is unset when no emails have been received yet
+                            m.usage = (u && u.size) || 0;
+                        });
 
                         callback();
                     });