4.0版本，联合主键save时报错Cannot access offset of type array on array

[cs99619]

经跟踪src/Model.php文件941行错误
将原来代码

        if ($this->key) {
            $where = [$pk => $this->key];
        } elseif (is_string($pk) && isset($this->origin[$pk])) {
            $where     = [$pk => $this->origin[$pk]];
            $this->key = $this->origin[$pk];
        } elseif (is_array($pk)) {
            foreach ($pk as $field) {
                if (isset($this->origin[$field])) {
                    $where[] = [$field, '=', $this->origin[$field]];
                }
            }
        }

修改为：

        if ($this->key) {
            if (is_array($this->key)) {
                foreach ($this->key as $field) {
                    if (isset($this->origin[$field])) {
                        $where[] = [$field, '=', $this->origin[$field]];
                    }
                }
            } else {
                $where = [$pk => $this->key];
            }
        } elseif (is_string($pk) && isset($this->origin[$pk])) {
            $where     = [$pk => $this->origin[$pk]];
            $this->key = $this->origin[$pk];
        } elseif (is_array($pk)) {
            foreach ($pk as $field) {
                if (isset($this->origin[$field])) {
                    $where[] = [$field, '=', $this->origin[$field]];
                }
            }
        }