Clear mysql error in fetch_into

ext/mysqli/mysqli.c

@@ -731,7 +731,7 @@ void php_mysqli_fetch_into_hash_aux(zval *return_value, MYSQL_RES * result, zend
 	/* TODO: We don't have access to the connection object at this point, so we use low-level
 	 * mysqlnd APIs to access the error information. We should try to pass through the connection
 	 * object instead. */
-	if (MyG(report_mode) & MYSQLI_REPORT_ERROR) {
+	if (MyG(report_mode) & MYSQLI_REPORT_ERROR && result->conn) {
 		MYSQLND_CONN_DATA *conn = result->conn;
 		unsigned error_no = conn->m->get_error_no(conn);
 		if (error_no) {

ext/mysqli/tests/gh14255.phpt

@@ -0,0 +1,31 @@
+--TEST--
+Bug GH-14255 (mysqli_fetch_assoc reports error from nested query)
+--EXTENSIONS--
+mysqli
+--SKIPIF--
+<?php
+require_once 'skipifconnectfailure.inc';
+?>
+--FILE--
+<?php
+
+require_once 'connect.inc';
+
+mysqli_report(MYSQLI_REPORT_STRICT|MYSQLI_REPORT_ERROR);
+
+$mysqli = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
+
+$ca = $mysqli->query('SELECT 1 ');
+$c = $ca->fetch_assoc();
+try {
+    $mysqli->query('SELECT non_existent_column');
+} catch (Exception $e) {
+    echo "Caught exception"."\n";
+}
+$c = $ca->fetch_assoc();
+
+print "done!";
+?>
+--EXPECTF--
+Caught exception
+done!

ext/mysqlnd/mysqlnd_result.c

@@ -972,6 +972,13 @@ MYSQLND_METHOD(mysqlnd_res, fetch_into)(MYSQLND_RES * result, const unsigned int
 	bool fetched_anything;
 	zval *row_data;
 
+	// We clean the error here because in unbuffered mode we could receive a new error
+	// and therefore consumers of this method are checking for errors
+	MYSQLND_CONN_DATA *conn = result->conn;
+	if (conn) {
+		SET_EMPTY_ERROR(conn->error_info);
+	}
+
 	DBG_ENTER("mysqlnd_res::fetch_into");
 	if (FAIL == result->m.fetch_row(result, &row_data, flags, &fetched_anything)) {
 		RETVAL_FALSE;