pgsql: Fix nested error handling in PG_FINALLY

Fix nested error handling in PG_FINALLY

We need to pop the error stack before running the user-supplied
PG_FINALLY code.  Otherwise an error in the cleanup code would end up
at the same sigsetjmp() invocation and result in an infinite error
handling loop.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/95a822c3-728b-af0e-d7e5-71890507ae0c%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/581a55889ba7f76dd87a270e37e5137f684bfdb7

Modified Files
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src/backend/utils/adt/xml.c | 2 +-
src/include/utils/elog.h    | 8 +++++---
2 files changed, 6 insertions(+), 4 deletions(-)