Ensure send message button does not appear when message box not available
Ensure send message button does not appear when message box not available

Fixes a regression introduced by commit faa71c9e16c6f036b298dd563da35eee38d861ca

Has resulted in confusion for users since the existence of the
button without the message box means there is nothing to send
which results in an error.

This only appears to affect Litigator interim claims as
they are not redeterminable.

ministryofjustice/advocate-defence-payments,ministryofjustice/advocate-defence-payments,ministryofjustice/advocate-defence-payments,ministryofjustice/advocate-defence-payments