pgsql: Fix another ancient bug in parsing of BRE-mode regular expressio

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

While poking at the regex code, I happened to notice that the bug
squashed in commit afcc8772e had a sibling: next() failed to return
a specific value associated with the '}' token for a "\{m,n\}"
quantifier when parsing in basic RE mode. Again, this could result
in treating the quantifier as non-greedy, which it never should be in
basic mode. For that to happen, the last character before "\}" that
sets "nextvalue" would have to set it to zero, or it'd have to have
accidentally been zero from the start. The failure can be provoked
repeatably with, for example, a bound ending in digit "0".

Like the previous patch, back-patch all the way.

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/bf9d3a5f847e91154b7cde255da7f24cd129ff35

Modified Files
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src/backend/regex/regc_lex.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)