Bug 16682: Fix display if Batch patron modification tool does not get any patrons

Bug 16682: Fix display if Batch patron modification tool does not get any patrons

To reproduce:
- Go to Tools->Batch patron modification
- Submit without filling any of  "Use a file", "Or use a patron list",
  "Or list card numbers..." or use a patron lists with zero members
Result: Screen without any information

To test:
- Apply patch
- Repeat steps above
- Verify that you get a nice message
- Verify that the tool works as before
  - with invalid card numbers only
  - with valid and invalid card numbers
  - with valid card numbers only

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>