Fix SSL_read/write return value checking in ma_tls_async_check_result

SSL_{read,write}'s return values == 0 signify the operation was
unsuccessful, but here it's being treated as success. Other calls of
these functions already properly checks the return value.

Signed-off-by: Josh Hunt <[email protected]>

libmariadb/secure/openssl.c

@@ -533,7 +533,7 @@ ma_tls_async_check_result(int res, struct mysql_async_context *b, SSL *ssl)
 {
   int ssl_err;
   b->events_to_wait_for= 0;
-  if (res >= 0)
+  if (res > 0)
     return 1;
   ssl_err= SSL_get_error(ssl, res);
   if (ssl_err == SSL_ERROR_WANT_READ)