Possible Isue with RedisPersistenceProvider.GetWorkflowInstance

**Describe the bug**
raw variable, obtained from redis_HashGetAsync may not have data and JsonConvert will throw an exception.

Issue was found in the log showing that IndexConsumer.ProcessItem is throwing an error "Error indexing workfow - XXX- Value cannot be null. (Parameter 'value'). Note that ElasticSearch is not used, so the IndexConsumer will be using default ISearchIndex implementation

**To Reproduce**
Steps to reproduce the behavior:
It happens pretty often. Not sure on the steps to reproduce. Maybe the workflow has been removed when the IndexConsumer runs.
**Expected behavior**
It should not throw an exception when workflow cannot be found.

**Additional context**
Add any other context about the problem here.