Handle errors during PDO row fetch

The EOF flag also gets set on error, so we always end up ignoring
errors here.

However, we should only check errors for unbuffered results. For
buffered results, this function is guaranteed not to error, and
querying the errno may return an unrelated error.

ext/pdo_mysql/mysql_statement.c

@@ -668,11 +668,7 @@ static int pdo_mysql_stmt_fetch(pdo_stmt_t *stmt, enum pdo_fetch_orientation ori
 #endif /* PDO_USE_MYSQLND */
 
 	if ((S->current_data = mysql_fetch_row(S->result)) == NULL) {
-#if PDO_USE_MYSQLND
-		if (S->result->unbuf && !S->result->unbuf->eof_reached && mysql_errno(S->H->server)) {
-#else
-		if (!S->result->eof && mysql_errno(S->H->server)) {
-#endif
+		if (!S->H->buffered && mysql_errno(S->H->server)) {
 			pdo_mysql_error_stmt(stmt);
 		}
 		PDO_DBG_RETURN(0);