Fix memory sanitizer error under MDCT_STEREO_PLC_FADE_2_BG_NOISE
Fixes use-of-uninitialized value in rate switching scenario with PLC.
See https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/jobs/35369.
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Fixes use-of-uninitialized value in rate switching scenario with PLC.
See https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/jobs/35369.