Fix 8101b33 to decode ignored redundancy

Even if the redundancy is ignored, the final range from the decoder is
needed for testing.

Reviewed by Timothy B. Terriberry.

src/opus_decoder.c

@@ -455,10 +455,6 @@ static int opus_decode_frame(OpusDecoder *st, const unsigned char *data,
    {
       transition = 0;
       pcm_transition_silk_size=ALLOC_NONE;
-      /* don't use stale CELT decoder to decode second redundancy frame if
-         the first redundancy frame for a transition from SILK was lost */
-      if (celt_to_silk && st->prev_mode == MODE_SILK_ONLY && !st->prev_redundancy)
-         redundancy = 0;
    }
 
    ALLOC(pcm_transition_silk, pcm_transition_silk_size, opus_val16);
@@ -504,6 +500,11 @@ static int opus_decode_frame(OpusDecoder *st, const unsigned char *data,
    /* 5 ms redundant frame for CELT->SILK*/
    if (redundancy && celt_to_silk)
    {
+      /* If the previous frame did not use CELT (the first redundancy frame in
+         a transition from SILK may have been lost) then the CELT decoder is
+         stale at this point and the redundancy audio is not useful, however
+         the final range is still needed (for testing), so the redundancy is
+         always decoded but the decoded audio may not be used */
       MUST_SUCCEED(celt_decoder_ctl(celt_dec, CELT_SET_START_BAND(0)));
       celt_decode_with_ec(celt_dec, data+len, redundancy_bytes,
                           redundant_audio, F5, NULL, 0);
@@ -566,7 +567,10 @@ static int opus_decode_frame(OpusDecoder *st, const unsigned char *data,
       smooth_fade(pcm+st->channels*(frame_size-F2_5), redundant_audio+st->channels*F2_5,
                   pcm+st->channels*(frame_size-F2_5), F2_5, st->channels, window, st->Fs);
    }
-   if (redundancy && celt_to_silk)
+   /* 5ms redundant frame for CELT->SILK; ignore if the previous frame did not
+      use CELT (the first redundancy frame in a transition from SILK may have
+      been lost) */
+   if (redundancy && celt_to_silk && (st->prev_mode != MODE_SILK_ONLY || st->prev_redundancy))
    {
       for (c=0;c<st->channels;c++)
       {