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Account for redundancy signalling when computing st->silk_mode.maxBits

Without that, we could bust the budget and end up with the
if (ec_tell(&enc) <= 8*nb_compr_bytes)
being false, followed by an assert failure later.

--- a/src/opus_encoder.c

+++ b/src/opus_encoder.c

@@ -1894,14 +1894,21 @@

         st->silk_mode.useCBR = !st->use_vbr;

         /* Call SILK encoder for the low band */

-        nBytes = IMIN(1275, max_data_bytes-1-redundancy_bytes);

-        st->silk_mode.maxBits = nBytes*8;

+        /* Max bits for SILK, counting ToC, redundancy bytes, and optionally redundancy. */

+        st->silk_mode.maxBits = IMIN(1275, max_data_bytes-1-redundancy_bytes)*8;

+        if (redundancy)

+        {

+           /* Counting 1 bit for redundancy position and 20 bits for flag+size (only for hybrid). */

+           st->silk_mode.maxBits -= 1;

+           if (st->mode == MODE_HYBRID)

+              st->silk_mode.maxBits -= 20;

+        }

         if (st->silk_mode.useCBR)

         {

            if (st->mode == MODE_HYBRID)

            {

-              st->silk_mode.maxBits = st->silk_mode.bitRate * frame_size / st->Fs;

+              st->silk_mode.maxBits = IMIN(st->silk_mode.maxBits, st->silk_mode.bitRate * frame_size / st->Fs);

            }

         } else {

            /* Constrained VBR. */

@@ -1908,7 +1915,7 @@

            if (st->mode == MODE_HYBRID)

            {

               /* Compute SILK bitrate corresponding to the max total bits available */

-              opus_int32 maxBitRate = compute_silk_rate_for_hybrid(nBytes*8*st->Fs / frame_size,

+              opus_int32 maxBitRate = compute_silk_rate_for_hybrid(st->silk_mode.maxBits*st->Fs / frame_size,

                     curr_bandwidth, st->Fs == 50 * frame_size, st->use_vbr, st->silk_mode.LBRR_coded);

               st->silk_mode.maxBits = maxBitRate * frame_size / st->Fs;

            }