Put SSL_pending() call behind the new internal SSL API.

It seems likely that any SSL implementation will need a similar call, not
just OpenSSL.

src/interfaces/libpq/fe-misc.c

@@ -1054,9 +1054,9 @@ pqSocketCheck(PGconn *conn, int forRead, int forWrite, time_t end_time)
 		return -1;
 	}
 
-#ifdef USE_OPENSSL
+#ifdef USE_SSL
 	/* Check for SSL library buffering read bytes */
-	if (forRead && conn->ssl && SSL_pending(conn->ssl) > 0)
+	if (forRead && conn->ssl_in_use && pgtls_read_pending(conn) > 0)
 	{
 		/* short-circuit the select */
 		return 1;

src/interfaces/libpq/fe-secure-openssl.c

@@ -186,6 +186,15 @@ pgtls_open_client(PGconn *conn)
 	return open_client_SSL(conn);
 }
 
+/*
+ *  Is there unread data waiting in the SSL read buffer?
+ */
+bool
+pgtls_read_pending(PGconn *conn)
+{
+	return SSL_pending(conn->ssl);
+}
+
 /*
  *	Read data from a secure connection.
  *

src/interfaces/libpq/libpq-int.h

@@ -641,6 +641,7 @@ extern int pgtls_init(PGconn *conn);
 extern PostgresPollingStatusType pgtls_open_client(PGconn *conn);
 extern void pgtls_close(PGconn *conn);
 extern ssize_t pgtls_read(PGconn *conn, void *ptr, size_t len);
+extern bool pgtls_read_pending(PGconn *conn);
 extern ssize_t pgtls_write(PGconn *conn, const void *ptr, size_t len);
 
 /*