Bug 34448: Update the way we handle response in http-client.js

Bug 34448: Update the way we handle response in http-client.js

Test plan:
Before patch:
- Visit a non-existent ID i.e. /cgi-bin/koha/erm/agreements/999
- Visit a char ID i.e. /cgi-bin/koha/erm/agreements/abc

Apply patch:
Repeat above steps.

Run cypress tests

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 2a0fcd9ddacf7bce25912778746f9994c06cdabe)
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>