bugfix !165 Juniper forms handling

bugfix !165 Juniper forms handling

I missed a small piece of my original "fix for forms with 'id' but no 'name'" (this one:
https://gitlab.com/openconnect/openconnect/-/commit/c8a6ee94180a09339eafefe0a2d889e7aa508e56#5503a3e92468be6db7c76e16b82bb5f3e9b14131_260_259)
in rebasing the ppp_core branch to merge cleanly with the changes from !171.

Caused this crash: https://gitlab.com/openconnect/openconnect/-/merge_requests/169#note_540411103

TODO: add Flask-based tests of Juniper auth to verify Juniper form handling.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>