Added null checks on context messages

[AndyButland]

Description

Not 100% sure if this is a useful guard or masking an underlying issue, but in investigating issues with nested blocks and validation on a customer database I found lots of errors like the following:

validation.controller.ts:58 Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'addTranslator')
    at et.addTranslator (validation.controller.ts:58:17)
    at UmbContextConsumerController.<anonymous> (validation-path-translator-base.controller.ts:19:12)
    at UmbContextConsumerController.setInstance (context-consumer.js:92:25)
    at UmbContextConsumer._onResponse [as callback] (context-consumer.js:43:22)
    at #handleContextRequest (context-provider.js:61:56)
    at UmbContextConsumerController.request (context-consumer.js:122:85)
    at UmbContextConsumerController.hostConnected (context-consumer.js:128:14)
    at controller-host.mixin.js:85:54
    at Array.forEach (<anonymous>)
    at l.hostConnected (controller-host.mixin.js:85:31)

observe-validation-state.controller.ts:17 Uncaught TypeError: Cannot read properties of undefined (reading 'hasMessagesOfPathAndDescendant')
    at UmbContextConsumerController.<anonymous> (observe-validation-state.controller.ts:17:35)
    at UmbContextConsumerController.setInstance (context-consumer.js:92:25)
    at UmbContextConsumer._onResponse [as callback] (context-consumer.js:43:22)
    at #handleContextRequest (context-provider.js:61:56)
    at UmbContextConsumerController.request (context-consumer.js:122:85)
    at UmbContextConsumerController.hostConnected (context-consumer.js:128:14)
    at controller-host.mixin.js:85:54
    at Array.forEach (<anonymous>)
    at Mt.hostConnected (controller-host.mixin.js:85:31)
    at controller-host.mixin.js:85:54

form-control-validator.controller.ts:33 Uncaught TypeError: Cannot read properties of undefined (reading 'getHasMessagesOfPathAndDescendant')
    at UmbContextConsumerController.<anonymous> (form-control-validator.controller.ts:33:37)
    at UmbContextConsumerController.setInstance (context-consumer.js:92:25)
    at UmbContextConsumer._onResponse [as callback] (context-consumer.js:43:22)
    at #handleContextRequest (context-provider.js:61:56)
    at UmbContextConsumerController.request (context-consumer.js:122:85)
    at UmbContextConsumerController.hostConnected (context-consumer.js:128:14)
    at controller-host.mixin.js:85:54
    at Array.forEach (<anonymous>)
    at xt.hostConnected (controller-host.mixin.js:85:31)
    at xt.hostConnected (form-control-validator.controller.ts:84:9)

I've resolved in this PR with null checks on the context.messages element that is undefined in some situations.