Resolve "Missing check in isar_render_poses()"

• Related issues: #2255 (closed)
• Requested reviewers: @tamarapu

Reason why this change is needed

• Missing check in isar_render_poses().
• Align the function with the float framework.

Description of the change

• Add missing check in isar_render_poses().
• Correct the length of the flushbuffer.

Affected operating points

• All is BE.

Closes #2255 (closed)