There is no server validation of incorrect Multiple and SRU-polymer S-Groups when User try to save it.

**Steps to Reproduce:**
1. Launch Ketcher.
2. Create the chain structure.
3. Sprout 3 chains from middle of structure.
4. Create Multiple S-Group with ends of chain sprouts. (Or SRU-polymer - the same behavior)
5. Click "Save" button.


**Expected Result:**
Before saving structure keeps Indigo validation, Indigo respond with error message and then User can save incorrect S-Group.

**Actual Result:**
Incorrect Multiple and SRU-group has only Ketcher's validation and User can't save it.
For Generic and Superatom S-Groups there is Indigo validation, but with incorrect message: "Structure contains one or more stereogenic atom(s) with unspecified stereochemistry"