openWriteStream: estimatedSize = 0 is ignored

[jaller94]

The following code may lead to unexpected results as obj is tested to not be falsy.

        let targetSource = false;
        for(const obj of [ _mode, _targetSource ])
            if(obj && obj.constructor === Boolean)
                targetSource = obj as boolean;

        let estimatedSize = -1;
        for(const obj of [ _mode, _targetSource, _estimatedSize ])
            if(obj && obj.constructor === Number)
                estimatedSize = obj as number;