Check if user is blocked during upload process

Check if user is blocked during upload process

Further down, this was already somewhat being checked.
On L112, `verifyTitlePermissions` is called, which will fail
if the user is blocked. However:

* This was not being checked during stashed uploads
* Block just "happens" to be part of that check: the intent is
  actually to verify the file title. The error is treated as
  recoverable (the title can be changed), but it isn't (the
  user can't unblock himself in this process)

Bug: T111228
Change-Id: I9cbf250a0b92c3daa3a0843f2257cc049abd3923