Nucleotide preset: APs don't become visible in the preset tab after deleting the bond connecting the base and sugar or sugar and phosphate

[MarinaKisacik]

Found while testing: #8996

Steps to Reproduce:

1. In Molecules mode, paste from the clipboard: CCCCCCCC.
2. Click Create a monomer button.
3. Select 'Nucleotide (preset)' type
4. Define a base, a sugar, and a phosphate (for instance, as shown in the screenshots below)

5. Delete the bond connecting the base and sugar
6. Switch to Preset tab and ensure that APs are now visible on the tab

Actual Result:
APs don't become visible in the preset tab

The same result after deleting the bond connecting the sugar and the phosphate.

Expected Result:
APs become visible in the preset tab

As per requirements in #8996 :

Found in Environment:

• Ketcher Version 3.16.0-rc.1 Build at 2026-05-06; 20:39:57
• Indigo Version 1.44.0-rc.3.0-g5ef48a5af-wasm32-wasm-clang-23.0.0
• Chrome Version 148.0.7778.97 (Official Build) (64-bit)
• Win11