eth/catalyst: fix edge case in simulated backend (#31871)

geth cmd: `geth --dev --dev.period 5`
call: `debug.setHead` to rollback several blocks.

If the `debug.setHead` call is delayed, it will trigger a panic with a
small probability, due to using the null point of
`fcResponse.PayloadID`.

---------

Co-authored-by: Marius van der Wijden <[email protected]>

Author: mask-pp

eth/catalyst/simulated_beacon.go

@@ -208,6 +208,12 @@ func (c *SimulatedBeacon) sealBlock(withdrawals []*types.Withdrawal, timestamp u
 		return errors.New("chain rewind prevented invocation of payload creation")
 	}
 
+	// If the payload was already known, we can skip the rest of the process.
+	// This edge case is possible due to a race condition between seal and debug.setHead.
+	if fcResponse.PayloadStatus.Status == engine.VALID && fcResponse.PayloadID == nil {
+		return nil
+	}
+
 	envelope, err := c.engineAPI.getPayload(*fcResponse.PayloadID, true)
 	if err != nil {
 		return err