pgsql: Fix ancient bug in parsing of BRE-mode regular expressions.

Fix ancient bug in parsing of BRE-mode regular expressions.

brenext(), when parsing a '*' quantifier, forgot to return any "value"
for the token; per the equivalent case in next(), it should return
value 1 to indicate that greedy rather than non-greedy behavior is
wanted.  The result is that the compiled regexp could behave like 'x*?'
rather than the intended 'x*', if we were unlucky enough to have
a zero in v->nextvalue at this point.  That seems to happen with some
reliability if we have '.*' at the beginning of a BRE-mode regexp,
although that depends on the initial contents of a stack-allocated
struct, so it's not guaranteed to fail.

Found by Alexander Lakhin using valgrind testing.  This bug seems
to be aboriginal in Spencer's code, so back-patch all the way.

Discussion: https://postgr.es/m/16814-6c5e3edd2bdf0d50@postgresql.org

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/afcc8772edcec687d87b6f762ca6113229af7291

Modified Files
--------------
src/backend/regex/regc_lex.c                        | 2 +-
src/test/modules/test_regex/expected/test_regex.out | 8 ++++++++
src/test/modules/test_regex/sql/test_regex.sql      | 2 ++
3 files changed, 11 insertions(+), 1 deletion(-)