[non-BE] Resolve "Counter st->Nb_ACELP_frames can overflow"

• Related issues: #1279 (closed)
• Requested reviewers: @vasilache

Reason why this change is needed

• Counter st->Nb_ACELP_frames can overflow

Description of the change

• Avoid possible overflow of counter st->Nb_ACELP_frames.

Affected operating points

• All is BE except for veeery long files without switching (no DTX, no TCX/HQ frames, etc.)