pgsql: Fix core dump in transformValuesClause when there are no columns

Fix core dump in transformValuesClause when there are no columns.

The parser code that transformed VALUES from row-oriented to
column-oriented lists failed if there were zero columns.
You can't write that straightforwardly (though probably you
should be able to), but the case can be reached by expanding
a "tab.*" reference to a zero-column table.

Per bug #17477 from Wang Ke. Back-patch to all supported branches.

Discussion: https://postgr.es/m/17477-0af3c6ac6b0a6ae0@postgresql.org

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/90e52884edf75b86c2832e6094d30eb2987d23a2

Modified Files
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src/backend/parser/analyze.c | 21 +++++++--------------
src/test/regress/expected/select.out | 7 +++++++
src/test/regress/sql/select.sql | 5 +++++
3 files changed, 19 insertions(+), 14 deletions(-)