Bug 14011: Triggering slip print with enter key collides with 'barcode submitted'

Bug 14011: Triggering slip print with enter key collides with 'barcode submitted'

To reproduce:

- Log into staff client
- Find a client with 0 checkouts
- Print a slip (or cancel printing it)
- Attempt to type in a barcode to checkout
  -- annoying modal screen pops up
     'barcode submitted' message will be triggered each time
     you try

To test:
- apply patch
- try to reproduce issue

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>