Resolve "[CLANG18] MSAN: use-of-uninitialized-value in lib_rend/ivas_dirac_dec_binaural_functions_fx.c:6583:59"

• Related issues: #2357 (closed)
• Requested reviewers: @kiene

Reason why this change is needed

• MSAN pointed out missing init.

Description of the change

• Added the missing init.

Affected operating points

• BE change unless CI has been using random init.

Closes #2357 (closed)