Fix for upload failure on multi sites

During development on our first multi site using EE3.4.3 we hit an error on all file uploads on any site but the original.

An upgrade to EE3.5.2, still resulted in the same error.

After a few hours of searching i found that by sending $ignore_site_id as TRUE in /system/ee/legacy/libraries/filemanager.php on line 2070, the error is removed, but not completely fixed.

For others who might be having the same problem open the file specified and change the line from

$thumb_info = $this->get_thumb($file['file_name'], $dir['id']);

to

$thumb_info = $this->get_thumb($file['file_name'], $dir['id'], TRUE);

and then with a synchronization of the file manager and the problem should be fixed.

The current problem seems to be that the legacy file upload function when using ee()->config->item(‘site_id’) always gets 1, even when on another multi site