[Patch] change the return value of PQsendFlushRequest

Hi all

The return value of function PQsendFlushRequest is 1 or 0.
-------------------------------------------------------------------
<para>
    Sends a request for the server to flush its output buffer.
<synopsis>
int PQsendFlushRequest(PGconn *conn);
</synopsis>
</para>

<para>
    Returns 1 for success.  Returns 0 on any failure.
</para>
---------------------------------------------------------------------
But in the following code, false is returned.
I think it would be better to change to 0.

int PQsendFlushRequest(PGconn *conn)
{
......
    if (conn->asyncStatus != PGASYNC_IDLE &&
        conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("another command is already in progress\n"));
        return false;  ※
    }
......
}

Best Regards!
Zhangjie