openssl: do not log excess "TLS app data" lines for TLS 1.3

The SSL_CTX_set_msg_callback callback is not just called for the
Handshake or Alert protocols, but also for the raw record header
(SSL3_RT_HEADER) and the decrypted inner record type
(SSL3_RT_INNER_CONTENT_TYPE). Be sure to ignore the latter to avoid
excess debug spam when using `curl -v` against a TLSv1.3-enabled server:

    * TLSv1.3 (IN), TLS app data, [no content] (0):

(Following this message, another callback for the decrypted
handshake/alert messages will be be present anyway.)

Closes https://github.com/curl/curl/pull/3281