opus_celt: Fix arithmetic overflow (per RFC8251)

As per Sec.8 of RFC8251:
    Cap on Band Energy
    NaN due to large log-energy value. Affects celt_denormalize().
Signed-off-by: Andrew D'Addesio <modchipv12@gmail.com>

libavcodec/opus_celt.c

@@ -481,7 +481,8 @@ static void celt_denormalize(CeltFrame *f, CeltBlock *block, float *data)
 
     for (i = f->start_band; i < f->end_band; i++) {
         float *dst = data + (ff_celt_freq_bands[i] << f->size);
-        float norm = exp2f(block->energy[i] + ff_celt_mean_energy[i]);
+        float log_norm = block->energy[i] + ff_celt_mean_energy[i];
+        float norm = exp2f(FFMIN(log_norm, 32.0f));
 
         for (j = 0; j < ff_celt_freq_range[i] << f->size; j++)
             dst[j] *= norm;