use better messaging when status list isn't available

[jchartrand]

As it stands, V+ shows this when the status list can't be retrieved at verification time:

Seems like we'd want to change that 'Has not been revoked by issuer' to instead say something like 'Could not check if the credential has been revoked.' and replace the green checkmark with a red X or something like

[jchartrand]

Same issue applies to the Learner Credential Wallet: openwallet-foundation-labs/learner-credential-wallet#642

[alexfigtree]

Done and deployed