[ValidatorSet] Handling 0-length of memory array

[nxqbao]

Description

Previous code does not handle updating size of revoked candidates array, which causes false emission of event CreditScoreUpdated(address(0)).

Contract changes

The table below shows the following info:

• Logic: the logic is changed.
• ABI: the ABI is changed.
• Init data: new storage field is declared and needs initializing.
• Dependent: needs to be changed due to changes in other contracts.

Contract name	Logic	ABI	Init data	Dependent
BridgeTracking
GovernanceAdmin
Maintenance
SlashIndicator
Staking
StakingVesting
ValidatorSet	[x]

Checklist

• I have clearly commented on all the main functions following the NatSpec Format
• The box that allows repo maintainers to update this PR is checked
• I tested locally to make sure this feature/fix works