initCallback is not called when first Ziti event is received

[scareything]

The CZiti class was using the state of its ziti_context property as a breadcrumb that was set when the first Ziti event was received. Recent changes in the initialization sequence for ziti-sdk-c resulted in the ziti_context being initialized before connecting to the controller, which meant that its state could not be used to determine if the first Ziti event was being processed.

Instead of using the ziti_context, simply add a boolean property to record when the first event is processed.