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

src/test/modules/test_regex/sql/test_regex.sql

@@ -214,6 +214,8 @@ select * from test_regex('a?*', '', '-');
 select * from test_regex('a+*', '', '-');
 -- expectError	7.15 -		a*+	BADRPT
 select * from test_regex('a*+', '', '-');
+-- test for ancient brenext() bug; not currently in Tcl
+select * from test_regex('.*b', 'aaabbb', 'b');
 
 -- doing 8 "braces"