Fixed #3595

[capone212]

#3595
Stopping heartbeat timer before remove

[capone212]

Pasted relevant conversation from issue #3595 for the sake of history.

Consider the following scenario:

1. Timer expires and timer handler (invalidateHeartbeat) scheduled for execution
2. The Timer is Reset-ed in resetHeartbeatTimerLockedafter client heartbeat
3. invalidateHeartbeat removes active timer from heartbeatTimers maps
4. client hearbeat inserts new active timer in resetHeartbeatTimerLocked
5. after leaked timer from step 3 expires, it calls invalidateHeartbeat which again leaks active timer from step 4, and essentially we are in circle loop from steps 3 to 5.

The net effect is client status flaps from down to ready constantly.

[github-actions]

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