Fix memory leak on NFC DH generation error path

It was possible for some NFC DH generation error paths to leak memory
since the old private/public key was not freed if an allocation failed.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/crypto/dh_group5.c

@@ -15,6 +15,7 @@
 
 void * dh5_init(struct wpabuf **priv, struct wpabuf **publ)
 {
+	wpabuf_free(*publ);
 	*publ = dh_init(dh_groups_get(5), priv);
 	if (*publ == NULL)
 		return NULL;