Fix SSL_export_keying_material() for DTLS1_BAD_VER

Commit d8e8590e ("Fix missing return value checks in SCTP") made the
DTLS handshake fail, even for non-SCTP connections, if
SSL_export_keying_material() fails. Which it does, for DTLS1_BAD_VER.

Apply the trivial fix to make it succeed, since there's no real reason
why it shouldn't even though we never need it.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>

ssl/ssl_lib.c

@@ -2300,7 +2300,7 @@ int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen,
                                const unsigned char *p, size_t plen,
                                int use_context)
 {
-    if (s->version < TLS1_VERSION)
+    if (s->version < TLS1_VERSION && s->version != DTLS1_BAD_VER)
         return -1;
 
     return s->method->ssl3_enc->export_keying_material(s, out, olen, label,