fix: create instance from custom iso

[mas-who]

Done

• Fixed issue when creating an instance from the custom ISO list, the redirect may result in invalid instance type locked for the instance creation page.

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @mas-who or @edlerd for access.
   • With a local copy of this branch, run as described here.
2. Perform the following QA steps:
   • upload foo.iso (from test fixtures), go to Storage -> Custom ISOs and try create an instance from the uploaded custom iso. No error should show (i.e. invalid instance type) when the instance gets created.

[webteam-app]

Demo starting at https://lxd-ui-696.demos.haus

[edlerd]

Good catch, thanks for fixing it :)