Future dates display as "now"

Steps to reproduce:

• Use two devices with a 1h clock offset
• Add both to a private group
• Exchange messages
• In the device which is behind, all messages will show a time of "now"

This is very confusing and makes it difficult to notice that the devices clocks are off.

Possible solution: show "invalid time" instead, to help the owner of the misconfigured device notice the issue.

The correct solution is #1098, but even if that were in place, there may be cases where this could help, and I can't think of it doing much damage.