Release cache tuple when no longer needed

Release cache tuple when no longer needed

There was a small buglet in commit 52e4f0cd472d whereby a tuple acquired
from cache was not released, giving rise to WARNING messages; fix that.

While at it, restructure the code a bit on stylistic grounds.

Author: Hou zj <[email protected]>
Reported-by: Peter Smith <[email protected]>
Reviewed-by: Amit Kapila <[email protected]>
Discussion: https://postgr.es/m/CAHut+PvKTyhTBtYCQsP6Ph7=o-oWRSX+v+PXXLXp81-o2bazig@mail.gmail.com