Bug 37464: Validate "type" sent to barcode/svc

Bug 37464: Validate "type" sent to barcode/svc

This change validates the "type" sent to the barcode/svc. Without this
change, we pass the user input directly to GD::Barcode, which passes
the input into an eval{} block without any validation of its own.

Test plan:
0. Apply the patch
1. koha-plack --reload kohadev
2. Go to http://localhost:8081/cgi-bin/koha/svc/barcode?type=bad&barcode=123456
3. Note that a Code39 barcode is provided for an invalid type
4. Go to http://localhost:8081/cgi-bin/koha/svc/barcode?type=Code39&barcode=123456
5. Note that a Code39 barcode is provided
6. Go to http://localhost:8081/cgi-bin/koha/svc/barcode?type=UPCE&barcode=123456
7. Note that a non-Code39 barcode is provided (presumably UPCE)

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>