Instead of a bare recv() to read the server's response to an SSL

Instead of a bare recv() to read the server's response to an SSL
request packet, use pqReadData().  This has the same effect since
conn->ssl isn't set yet and we aren't expecting more than one byte.
The advantage is that we will correctly detect loss-of-connection
instead of going into an infinite loop.  Per report from Hannu Krosing.