This happens because we were passing incorrect arguments to
ReorderBufferFinishPrepared().

Author: Masahiko Sawada
Reviewed-by: Vignesh C
Backpatch-through: 14
Discussion: https://postgr.es/m/CAD21AoBqhUqgDZUhUVnnwKRubPDNJ6m6fJDPgok3E5cWJLL+pA@mail.gmail.com