The notifications are not sent when bulk assigning issues

When assigning an issue the notification is sent, however when bulk assigning issues the notifications are not.

Steps to Reproduce:

1. Set your Notification Scheme to send an email to the current assignee when an issue is assigned. (as shown in the screenshot "NotificationScheme")
2. Assign an issue to the user e.g. User1.
   • The user will receive a notification. (See attached screenshot "SingleAssignment")
3. Bulk assign several issues to e.g. User2 (I tested assigning 3 at once)
   • The user will not receive any notifications.

(The names was just for example, you can assign all to the same users and he will only receive notifications when an issue is assigned without using bulk edit)