by Ângelo Rigo.
Thank you very much Mary Cooch!!
We apply the patch and it work fine for the screen where the student can pick the file, if he click on Save changes button having not picked any file the assignment is not marked as submited anymore, this is great!.
But he still have the button "Submit Assignment" into the "Submit Status" screen wich you can reach by clicking on the "Cancel" button, into this screen if you click the button "Submit Assignment" it does mark the assignment as submitted even have not pick any file.
I will report this on the same tracker issue : https://tracker.moodle.org/browse/MDL-36908
Cheers