[Non-BE] Resolve "JBM: Flushing of MCT can cause endless loop"

• Related issues: #999 (closed)
• Requested reviewers: @fotopoulou

Reason why this change is needed

A wrong condition in the flushing of MCT at a rate switch can cause an endless loop because the correct render function is not called.

Description of the change

Fix the condition. Add error case.

Affected operating points

• JBM Non-BE for RS with MCT and TD binaural object renderer as renderer for MCT
• Produced bitstream is BE compared to previous state (no encoder change).

Related to #999 (closed)