If reagents are on Canvas for cascade reaction, it can't be correctly saved to RXN/RDF

**Steps to Reproduce**
1. Add cascade reaction with reagent from ket:
[ketcher.zip](https://github.com/user-attachments/files/17344381/ketcher.zip)
2. Click on Save as...
3. Select RXN or RDF

**Actual behavior 1 - Save to RXN**
- Reaction 3:2 is displayed on preview because reagent is added to reactants and all products are united:

**Expected behavior 1 - Save to RXN**
- TBD - Only root reaction 1:1:1 with reagent is on preview and can be saved to RXN

**Actual behavior 2 - Save to RDF**
- Reaction 3:2 is displayed on preview because reagent is added to reactants and all products are united:

**Expected behavior 2 - Save to RDF**
- TBD - Two reactions 2:1 and 1:1 are displayed on preview and can be saved to RDF

**Environment details:**
- Ketcher [Version 2.26.0-rc.1] Build at 2024-10-04; 18:45:04
- Indigo Version 1.25.0-rc.1.0-g704673fcb-wasm32-wasm-clang-19.0.0
- Desktop, Windows 11 Enterprise
- Chrome Version 129.0.6668.100 (Official Build) (64-bit)

**Additional context**
- This test is added to xls file and **have to be automated**
- Issue could be related to other issues: https://github.com/epam/Indigo/issues/2412, https://github.com/epam/Indigo/issues/2424
- Issue is detected during exploratory testing of https://github.com/epam/Indigo/issues/2237