Bug 28135: Replace use of input type number in additem.js

Bug 28135: Replace use of input type number in additem.js

This patch corrects in instance where JavaScript is creating an input
tag with type "number."

To test, apply the patch and make sure the AcqCreateItem system
preference is set to "when receiving."

- Go to Acquisitions -> Vendor -> Invoices -> Invoice -> Go to receipt
  page -> Receive.
- On the page for receiving items you should see an add item form.
- Click the "Add multiple items" button at the bottom of the form.
- Test the "Number of items to add" field. It should not accept any
  input except numbers.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>