App crashes when entering a room after a call is hung-up just before being answered on the other end.

[langleyd]

App crashes when entering a room after a call is hung-up just before being answered on the other end.

It's difficult to reproduce the initial calling events that result in this issue.
Steps to reproduce the behaviour:

1. Join a DM with two users.
2. Request a call from one user.
3. Accept call on one side around the same time that you hangup on the other side.
4. Join this room with any iOS client.

Expected behaviour:
The app should not crash when joining the room but display the call history events.

Issue occurs just for iOS clients, on any iOS version.

Additional context
The problem is related to call timestamps, if the server returns a call start event time that is greater than the hangup time we get an integer overflow. The I think should gracefully handle this data as the other clients do.