Resolve "OSBA object-editing on uninitialized values"

• Related issues: #1322 (closed)
• Requested reviewers: @sagnowski

Reason why this change is needed

• More than necessary channels are allocated at the decoder/renderer, which results in operations on uninitialized values. *

Description of the change

• Correct the number of initialized float buffers (channels) at the decoder.
• Consequently, a memory reduction is also achieved.

Affected operating points

• All is BE.