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 <johunt@akamai.com>

libmariadb/mariadb_async.c

@@ -140,7 +140,7 @@ my_ssl_async_check_result(int res, struct mysql_async_context *b, MARIADB_SSL *c
 {
   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)

libmariadb/secure/openssl.c

@@ -529,7 +529,7 @@ 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)