BASOP assert in 48kbps stereo decoding due to left shift of negative value

Using item 26 of SQAM test set resampled to 48kbps,

./IVAS_cod_flt -stereo 48000 48 26_48kHz.wav bit
./IVAS_dec_fx stereo 48 bit out.wav

results in

Assertion failed: (0), function L_shl, file lib_com/basop32.c, line 2438.

in frame 1500. Caller context is `tcx_mdct_fx.c:305:

    FOR( i = 0; i < R2; i++ )
    {
        y[l + m + R2 + i] = round_fx( L_shl( Mpy_32_16_1( tmp_buf[L2 + i], fac ), s ) ); /* fold out right end of DCT */
    }

with i=6, fac=20066 and L2=30.