Preview: Unsplit monomer couldn't be saved to SMILES

[AlexeyGirin]

Steps to Reproduce

1. Go to Macromolecules mode - Flex mode
2. Open RNA tab - Nucleotides section
3. Put any monomers from that section to the canvas (it was 5AmdA in my case)
4. Switch to Micro mode
5. Save canvas to SMARTS

Actual behavior System throws an error: Convert error! Given string could not be loaded as (query or plain) molecule or reaction, see the error messages: 'RXN loader: bad header {', 'molecule: casting to molecule is invalid'

Expected behavior [H]-[#8]-[#6]/[#6]1-[#6](\[#8]-[#15](-[H])(-[#8])=[#8])-[#6]-[#6](/[#7]2-[#6]=[#7]-[#6]3-[#6](-[#7])=[#7]-[#6](-[#7])=[#7]-[#6]=3-2)-[#8]-1

Versions

• Ketcher Version 2.22.0-rc.2 Build at 2024-06-28; 05:30:15
• Indigo Toolkit Version 1.22.0-dev.2.1-gd5637f75-wasm32-wasm-clang-12.0.0
• Windows 10 Pro
• Chrome Version 126.0.6478.127 (Official Build) (64-bit)

Issue found while testing - https://github.com/epam/ketcher/issues/4382