Complex crash bug all started with this failure.
Diagnosed and fixed by Nikhil Sontakke, reviewed by me.

Reported-by: Jeff Janes
Author: Nikhil Sontakke
Discussion: https://postgr.es/m/CAMkU=1xBP8cqdS5eK8APHL=X6RHMMM2vG5g+QamduuTsyCwv9g@mail.gmail.com