Empty body of RNA (RNA1{}$$$$V2.0) is not a valid - error should occure

**NOTE**: Same problem for other polymer types: CHEM and PEPTIDE - have to be fixed in the same way

**Steps to Reproduce**
1. Go to Macromolecules mode - Flex mode
2. Load using paste from clipboard IDT type: `RNA1{}$$$$V2.0`

**Actual behavior**
System loads empty canvas

**Expected behavior**
System should show an error: RNA definition is missing (or something like that)

**Versions**
- Ketcher Version 2.23.0-rc.1 Build at 2024-07-02; 08:57:41
- Indigo Toolkit Version 1.22.0-rc.1.0-g2bef0ce6c-wasm32-wasm-clang-19.0.0
- Windows 10 Pro
- Chrome Version 126.0.6478.127 (Official Build) (64-bit)

Issue found while testing - https://github.com/epam/Indigo/issues/1188