Fixed usage of null WorkflowStep.Name in WorkflowActivity diagnostic service.

[jakenuts]

Describe the change
In WorkflowActivity.Enrich(WorkflowStep workflowStep) there was a check for a null or empty WorkflowStep.Name and "inline" was used in it's place in the activity display name. A line immediately after referenced WorkflowStep.Name without that check and causes a NullReferenceException if System.Diagnostics.ActivitySource & System.Diagnostics.Activity are used by the host or workflow implementation.

Describe your implementation or design

Replaced workflowStep.Name with stepName defined several lines above which either contains the name or "inline" for unnamed steps (Sagas, Snline, etc).

Tests
Did you cover your changes with tests? No.

Breaking change
Do you changes break compatibility with previous versions? No.

Additional context
As far as I can tell usage of ActivitySource and related services like OpenTelemetry are not possible while this bug remains.

[jakenuts]

Added additional nullable check for Body.Type.Name as that also is possibly null (End() step)