Bugfix multiple select

I have found a bug in the "upload" -> "Files":
If you select multiple files and then uncheck some of them, all files are being uploaded and not just the one that are checked when you click the upload button:
select t1,t2,t3
deselect t2,t3
-> all three files are being uploaded
Desired: only t1 is uploaded.

@davivel  Please review this minor changes.