SBL tag for data S-Groups is not supported in molfile V2000 loader

**Background
Loading of SBL-tag for data sgroups is not supported.
Data S-Group which doesn't contain any atoms defined by SAL but has only SBL considered to be empty and is not copied from one molecule to another.
Here is what specification says:

**Steps to Reproduce**
1. Load attached mol-example into Indigo
2. Save as ket

**Expected behavior**
Data S-Group should appear in KET-file

**Actual behavior**
Data S-Group is missing

**Attachments**
[sbl-dsgroup.zip](https://github.com/user-attachments/files/16488639/sbl-dsgroup.zip)