Search for SLRU page only in its own bank
One of the two slot scans in SlruSelectLRUPage was not walking only the
slots in the specific bank where the buffer could be; change it to do
that.
Oversight in
53c2a97a9266.
Author: Sergey Sargsyan <sergey.sargsyan.2001@gmail.com>
Discussion: https://postgr.es/m/18582-
5f301dd30ba91a38@postgresql.org