Resolve "[CLANG18] MSAN: use-of-uninitialized-value in lib_dec/dec_tcx_fx.c:1098:13"

• Related issues: #2383 (closed)
• Requested reviewers: @kiene

Reason why this change is needed

Avoid that an uninitialized Q_A_itf is being read, in case the ITF detector doesn't trigger.

Description of the change

Initialize Q_A_itf with default.

Affected operating points

All operating-point stay BE.

Closes #2383 (closed)