Preview: Export of unresolved monomer to everything except KET and IDT should cause specific error message (but it doesn't)

[AlexeyGirin]

Steps to Reproduce

1. Go to Macromolecules mode - Flex mode
2. Load using paste from clipboard IDT type: /i2AmPr/
3. Try to save canvas to MOL V3000 (and others unsupported - Sequence, FASTA, Mol V2000, SDF V2000, SDF V3000, SMARTS, SMILES, Extended SMILES, CML, InChl, InChI AuxInfo, InChIKey, CDXML, Base64 CDX, CDX)

Actual behavior System shows an error: Convert error! Given string could not be loaded as (query or plain) molecule or reaction, see the error messages: 'molecule json loader: Expected atoms block not found', 'RXN loader: bad header {', 'RXN loader: bad header {', 'molecule json loader: Expected atoms block not found'

Expected behavior System shows an error: Monomer /i2AmPr/ couldn't be saved to MDL Molfile V3000 format

As per requirements:

4. Attempt to save macromolecules with unknown monomers to file formats other than IDT and KET should result in error.
"Monomer /.../ couldn't be saved to .... format"

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/4431