[split-non-be] Reducing ISAR MD bitrate by removing redundant bits

• Related issues:
• Requested reviewers:

Reason why this change is needed

• #1073 (closed)

Description of the change

• Avoid coding of imaginary values in bands where they are going to be always zero.

Affected operating points

• IVAS output and bitstream BE
• ISAR bitstream and output non-BE