gnutls: retry handshake if it returns a non-fatal error

Based on the gnutls_handshake manual the function must be called again
until it returns 0 (or a fatal error).
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit ca82afbfb7ee9a083d13c7861408e5759f2509cd)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/misc/gnutls.c

@@ -242,9 +242,16 @@ static int gnutls_ContinueHandshake (vlc_tls_t *session)
 #ifdef WIN32
     WSASetLastError (0);
 #endif
+    do
+    {
         val = gnutls_handshake (sys->session);
+        msg_Dbg (session, "TLS handshake: %s", gnutls_strerror (val));
+
         if ((val == GNUTLS_E_AGAIN) || (val == GNUTLS_E_INTERRUPTED))
+            /* I/O event: return to caller's poll() loop */
             return 1 + gnutls_record_get_direction (sys->session);
+    }
+    while (val < 0 && !gnutls_error_is_fatal (val));
 
     if (val < 0)
     {