libpq: Fix inadvertent change in PQhost() behavior.

Commit 274bb2b3 caused PQhost() to
return the value of the hostaddr parameter rather than the relevant
host when the latter parameter was specified.  That's wrong.  Commit
9a1d0af4 then amplified the damage by
using PQhost() in more places, so that the SSL test suite started
failing.

Report by Andreas Karlsson; patch by me.

src/interfaces/libpq/fe-connect.c

@@ -5736,7 +5736,8 @@ PQhost(const PGconn *conn)
 {
 	if (!conn)
 		return NULL;
-	if (conn->connhost != NULL)
+	if (conn->connhost != NULL &&
+		conn->connhost[conn->whichhost].type != CHT_HOST_ADDRESS)
 		return conn->connhost[conn->whichhost].host;
 	else if (conn->pghost != NULL && conn->pghost[0] != '\0')
 		return conn->pghost;