Currently, `CIRCUIT_IS_ORIGIN()` actually looks at the purpose, not the base magic number: ``` #define CIRCUIT_IS_ORIGIN(c) (CIRCUIT_PURPOSE_IS_ORIGIN((c)->purpose)) ``` We should move it to look at the `magic` like `CIRCUIT_IS_ORCIRC()` is doing. The reason is because I was adding tracing events to the circuit subsystem and I kept having state transition event with a circuit global identifier of 0 which can't be because that value is set just after allocation. But at that point, the purpose has not been set so `CIRCUIT_IS_ORIGIN()` wasn't returning true. Furthermore, this made me discover another issue documented in legacy/trac#31608 where if we do make this change, we _must_ fix this ticket else we have a NULL deref.