Bug 19738: Fix XSS on vendor name in serials module

Bug 19738: Fix XSS on vendor name in serials module

Test plan:

1) do not apply this patch
2) Have at least one vendor which name does contain javascript, for
example: <i>Vendor 1</i><script>alert('Hi');</script>
3) go to serial module and create new subscription
4) use "Search for vendor"
5) Search for your vendor, when search results table is presented, the
javascript is executed
6) go through subscription creation and save the new subscription
7) On subscription detail page, the javascript is executed as well
8) apply this patch
9) Repeat 3-7, the script is not executed, the input is escaped

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>