Issue in dft stereo at 32 kbps for residual spectral lines decoding

with 7b78b916 and this bitstream :

ltv_STEREO_32k.bit.32000.zip

and the command line : STEREO 32 bit syn

As show un the figure below, a major problem can be seen in the synthesis.

After some debugging, it seems the problem come from that part of the code (in IVAS_Stereo_dft_dec_fx.c):

        IF( I != ECSQ_GLOBAL_GAIN_INDEX_ALL_ZERO )
        {
            ECSQ_init_instance_fx( &ecsq_inst, 0 /*dummy index*/, &range_uni_dec_state );

            rc_uni_dec_init_fx( &range_uni_dec_state, bit_stream_side + *nb_bits, max_bits - *nb_bits );

            hStereoDft->res_global_gain_fx = ECSQ_dequantize_gain_fx( I );
            move32();
#ifdef DEBUGGING
            dbgwrite_txt( (const float *) ( &hStereoDft->res_global_gain_fx ), 1, "fixed_res_global_gain.txt", NULL );
#endif

            ecsq_inst.config_index = sub( shl( hStereoDft->res_cod_mode[k_offset], 1 ), 1 );
            move16();

 >>>>>      ECSQ_decode( &ecsq_inst, hStereoDft->res_cod_line_max, dec );

>>>>>       n_bits = rc_uni_dec_virtual_finish_fx( &range_uni_dec_state ); 

            set_zero_fx( res_buf_fx, STEREO_DFT_N_8k );
            FOR( Word16 c = 0; c < hStereoDft->res_cod_line_max; c++ )
            {
                dec[c] = shl_sat( dec[c], 8 );
                move16();
            }

            ECSQ_dequantize_vector_fx( dec, hStereoDft->res_global_gain_fx, hStereoDft->res_cod_line_max, res_buf_fx );

#ifdef DEBUGGING
            dbgwrite_txt( (const float *) res_buf_fx, hStereoDft->res_cod_line_max, "fixed_res_buf.txt", NULL );
#endif
        }

ECSQ_decode( ..., ..., dec ); -> The last indice of dec is different between float and fix.

n_bits = rc_uni_dec_virtual_finish_fx( ... ); -> here it is not the same function as float, but using the "float" doesn't solve the problem as the n_bits output is the same (and wrong compared to float)

Given n_bits differs from float, it leads to a wrong bitstream decoding for the core decoder, which is likely the cause of the bad synthesis.

This is happening at frame 2769. @multrus, @norvell, I'm not sure who knows more about ECSQ coding, please feel free to tag someone else