pgsql: In PQsendQueryStart(), avoid leaking any left-over async result.

In PQsendQueryStart(), avoid leaking any left-over async result.

Ordinarily there would not be an async result sitting around at this
point, but it appears that in corner cases there can be.  Considering
all the work we're about to launch, it's hardly going to cost anything
noticeable to check.

It's been like this forever, so back-patch to all supported branches.

Report: <CAD-Qf1eLUtBOTPXyFQGW-4eEsop31tVVdZPu4kL9pbQ6tJPO8g@mail.gmail.com>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/886f6c5ccdb500eeeec7e0abdf1500e20a304c45

Modified Files
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src/interfaces/libpq/fe-exec.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)