eth/catalyst: fix a bug about using null PayLoadID

[mask-pp]

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.

[jwasinger]

Thanks for reporting this. Please attach a stack trace if possible.

[mask-pp]

Thanks for reporting this. Please attach a stack trace if possible.

Debug.SetHead` can only delay if there are a large number of blocks in the database. So, to capture this scenario I added sleep 500 ms. The longer the delay, the greater the probability of occurrence.

[jwasinger]

so iiuc, the issue is that if setHead has a delay, a block can be mined in the meantime while setHead is executing? and this will cause the crash?

[mask-pp]

so iiuc, the issue is that if setHead has a delay, a block can be mined in the meantime while setHead is executing? and this will cause the crash?

Yeah, and the forkchoiceUpdated returned here.