Resolve "[CLANG18] MSAN: use-of-uninitialized-value in lib_dec/ivas_stereo_mdct_core_dec_fx.c:392:9"

• Related issues: #2397 (closed)
• Requested reviewers: @multrus

Reason why this change is needed

• Fix from #2382 (closed) was missing an IF to not copy anything if bfi is set

Description of the change

• Add the missing condition

Affected operating points

• everything with MDCT-STereo core when concealment is triggered
• should be BE - uninit values were copied, but never actually used for anything

Closes #2397 (closed)