Reusable block: Crash when trying to convert to regular blocks a undefined/deleted reusable block

[fluiddot]

Sentry event: https://a8c.sentry.io/share/issue/1088c69e108447dda510460e139d0cb0/

Describe the bug
A crash is produced when converting to regular blocks an undefined or deleted reusable block. Undefined/deleted reusable blocks shouldn't allow this option so we need to remove it.

To Reproduce
Steps to reproduce the behavior:

1. Add an undefined reusable block. This can be done by adding the following HTML code to a post:

<!-- wp:block {"ref":-1} /-->

2. Observe that the block displays a message stating that is deleted or unavailable.
3. Select the block.
4. Tap on the three dots button to open the block options.
5. Tap on "Convert to regular blocks".
6. Observe that the app crashes.

Expected behavior
The "Convert to regular blocks" shouldn't be available on undefined/deleted reusable blocks.

Screenshots
N/A

Smartphone (please complete the following information):

• Device: iPhone 11
• OS: iOS 15.4.1
• Version 22.3.0.1

Additional context
N/A