"Activity" column  with the time since last activity can be negative
I have negative times for "last activity" column on the forum. 


![nim_forum_bug](https://user-images.githubusercontent.com/35006197/118532736-9547be00-b747-11eb-9551-37c49056ccbd.PNG)

This was caused by Windows changing the time zone of my computer in the last update - using the correct timezone on Windows fixed the bug. 
Still, I don't think displaying negative duration is the correct behaviour and it dishonor ``std/times`` 😛 .

