Fix some compiler warnings on older compilers
Some older compilers appear to not understand the recently introduced
PG_FINALLY code structure that well in some circumstances and complain
about possibly uninitialized variables. So to fix, initialize the
variables explicitly in the cases complained about.
Discussion: https://www.postgresql.org/message-id/flat/
95a822c3-728b-af0e-d7e5-
71890507ae0c%402ndquadrant.com