Discrete ISM gain calculation not done on the correct number of objects

Basic info

• Commit SHA: 7097cb8f
• Platform:

Bug description

The digest function for ISM with discrete objects does the gain calculation with a wrong number of objects for combined formats, since it uses the number of transport channels as number of objects and not the distinct number of objects available in the main decoder struct.

Ways to reproduce

(Clear steps or refer to a failing automated test, e.g. with a pipeline link)