Resolve "TypeError: Unable to get property 'form' of undefined or null reference"

What does this MR do?

Fixes: https://sentry.gitlap.com/gitlab/gitlabcom-clientside/issues/30927/

This error occurs when an issues#index or similar shows an empty state and we're always expecting a filtered-search box, so this will error if the filtered_search box isn't available. Non critical bug.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #32532 (moved)