The block template thumbnail path in block admin wrong for sites with Silverstripe in subdirectory

[mephzara]

On a site where Silverstripe is located in a subdirectory the template thumbnails are not shown in the admin interface. That's because the file detection uses the path on the server (which is working) but constructs a wrong URL for the browser. The subdirectory is missing.

A possible solution would be to change the line 133 in file Block.php from
$imgsrc = "/themes/".$theme."/templates/BlockTemplates/";
to
$imgsrc = Director::absoluteBaseURL()."themes/".$theme."/templates/BlockTemplates/";

Best regards