`UpdateState` panics if client message is of type `Misbehaviour`

[crodriguezvega]

Many thanks to @plafer for finding this bug.

Summary of Bug

It is possible for CheckForMisbehaviour to return false for a client message of type Misbehaviour, and if this happens, then UpdateState will panic.

Expected Behaviour

UpdateState does not panic if client message is of type Misbehaviour.

Version

v7.0.0

Steps to Reproduce

Submit an MsgUpdateClient where ClientMessage is of type Misbehaviour and contains two valid headers (e.g. two headers where Header1 has a higher height and later timestamp than Header2).

Proposed Solution

If the client message received by UpdateState if of type Misbehaviour then no-op (return []exported.Height{}). This solution is preferred at this moment because it is not API breaking.

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[colin-axner]

Required for #6232

The logic is: if a user submits a valid client message using the misbehaviour type (two headers) which is not actually misbehaviour, then there are no updates to perform (noop)