Directly accessing new reservation page with empty cart causes Rails error [v5.5]

[AlanLiu96]

Steps to reproduce:

1. empty your cart
2. in your browser url go to "[reservations URL]/reservations/new"

Expected Result:
redirected to catalog

Actual result:

Looks like the fix would be to redirect to catalog if back isn't set.
Might be related to #1235

[orenyk]

Good catch, this is simple enough that we should be able to swing it into v5.5.6.

[zeffman]

The error seems to have been fixed