We don't allow setting notifications to unread anymore so also prevent state issues when decreasing the counter

src/js/main.js

@@ -71,8 +71,9 @@ angular.module('Application').controller('MainController', ['$scope', '$route',
     }
 
     // update state of acknowledged notification
-    $scope.notificationAcknowledged = function (ack) {
-        $scope.notificationCount += (ack ? -1 : +1);
+    $scope.notificationAcknowledged = function () {
+        if ($scope.notificationCount === 0) return; // already down to 0
+        $scope.notificationCount--;
     };
 
     function init() {