[7.0] Project / Task / 'Assigned to' event sends notification about the previous event

[Tamás Reinhardt]

Please find the screenshot attached. You can see 3 phase of the task history. The bottom one is the first one and the top one is the last one in time.

How the bug can be reproduced:
1.) Log in as Administrator, create a project and add two followers to it.
2.) Create a task in the project and save it.
3.) Edit the task, remove the assignment (delete the content of the "Assigned to" field) and save it.
4.) Edit the task, assign it to an user and save it. It did not send the notification about the latest event but the previous one. The user will get a notification about "Assigned to: Administrator ->" instead of "Assigned to: Test user".
5.) Edit the task, assign it to another user and save it. The user got notified about the previous event again.