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>