Deselecting a bone or sub-bone in the viewer hides the info instead of showing parent info

Bug description and expected behavior

A clear and concise description of what the bug is, and what you expected to happen.

In the viewer, if the user selects a boneset from the dropdown, the boneset information (descriptions and image) is shown. When the user selects a bone, the bone information is shown. So, deselecting the bone should then show the boneset information again, but instead all the information is hidden:

https://github.com/user-attachments/assets/879171a2-ae0c-4d96-9d20-01f690b7f80e

Similarly, selecting a sub-bone and then deselecting it should display the information of the parent bone, but instead all of the information is hidden:

https://github.com/user-attachments/assets/2fab482d-bb3c-4961-9c04-448174134df2

Steps to reproduce

A list of steps it takes to see this bug.

1. Select a boneset from the dropdown. The boneset information will be displayed.
2. Select a bone from the dropdown. The bone information will be shown in place of the boneset information.
3. Change the bone selection back to the default, effectively deselecting the bone. It should revert back to the previous display, where the boneset information was shown, but instead all the information goes away completely.

Acceptance Criteria

A checklist of conditions that must be met for this task to be considered complete. How will we verify that it's done correctly?

• The buggy behavior no longer occurs.
• All related code passes the repository's workflow checks (linting, tests).
• The application runs without new errors after the changes are made.
• (If applicable) New automated tests have been added to cover the changes.

Additional context

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Start at the viewer's boneset, bone, and sub-bone selection handling described in the reproduction steps, and trace how the default selection determines the displayed information. Verify that deselecting a bone restores boneset information and deselecting a sub-bone restores parent-bone information, then run the repository workflow checks and confirm the application has no new errors.