Why not set builder->next_phase_at=InvalidTransactionId in SnapBuildRestore function?

[zxwsbg]

Last email has some problem, I resend one.
 
In PG14 or higher version, I notice that SnapBuildRestore function don't set 
builder->next_phase_at=InvalidTransactionId .
 
But in SnapBuildSerialize function, the assert check this condition.
 
Assert(builder->next_phase_at == InvalidTransactionId);
 
I'd like to know is this right?
 
Thanks.