Previously when inheriting category auto-close settings for a topic, those settings were disrupted if another topic timer was assigned or if a topic was closed then manually re-opened.
This PR makes it so that when a topic is manually re-opened the topic auto-close settings are inherited from the category. However, they will now be based on the topic created_at date. As an example, for a topic with a category auto close hours setting of 72 (3 days):
* Topic was created on 2021-02-15 08:00
* Topic was closed on 2021-02-16 10:00
* Topic was opened again on 2021-02-17 06:00
Now, the topic will inherit the auto close timer again and will close automatically at **2021-02-18 08:00**, which is based on the creation date. If the current date and time is greater than the original auto-close time (e.g. we were at 2021-02-20 13:45) then no auto-close timer is created.
Note, this will not happen if the topic category auto-close setting is "based on last post".
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