[Non-BE] Resolve "MSAN: use-of-uninitialized-value in ISM4 rate switching with JBM"

• Related issues: #1021 (closed), #1014 (closed), #1029 (closed)
• Requested reviewers:

Reason why this change is needed

In ISM to BINAURAL_ROOM_IR with JBM a case of unitialized memory can happen in the flush function at a rate switch from discrete to paramtric ISM. Caused by determining an update of the TC buffer subframe info based on the renderer type in the main decoder struct which is already set to the one used for ParamISM at this point. This is a follow up to #1014 (closed), because the fix in !1425 (merged) was not enough

Description of the change

Use the correct renderer type, i.e. the previous one for discrete ISM in this case. For this, add a distinct function parameter for the renderer type for the discrete ism renderer. Additionally the determination of the number of objects to be processed is fixed for the discrete ISM renderer.

Affected operating points

• Non-BE for ISM with rate switching and JBM
• Produced bitstream is BE compared to previous state (no encoder change).

Related to #1021 (closed)