Check active channel is CLOSED when reopening an ICA channel

[crodriguezvega]

We should check here that the channel is not closed instead, because it could be possible to reopen a channel that is going through an upgrade (in FLUSHING or FLUSH_COMPLETE state).

Thinking now if we should change this condition to channel.State != channeltypes.CLOSED... I am thinking of the following scenario: an ICA channel is going through a channel upgrade and the channel state is either FLUSHING or FLUSH_COMPLETE, and a relayer submits a MsgChannelOpenInit with the same metadata version as the channel going through the upgrade. With the current check the opening handshake would go through, right? I guess we should prevent that?
If we need to change this, we can do it in a follow up PR.

Originally posted by @crodriguezvega in #5562 (comment)

[DimitrisJim]

done in #5601