spec not aligned with VTM6 code on lfnst idx conditions (sec 7.3.8.5)

[fabrice.leleannec]

The condition on the DCT2 transform type for LFNST index coding is not aligned with VTM6 software. In the software, the value tu_cbf_luma[x0][y0] is taken into account, which is not the case in the spec.

The condition should bebe change from tu_mts_idx[ x0 ][ y0 ] == 0 to :
(tu_mts_idx[ x0 ][ y0 ] == 0 \|\| !tu_cbf_luma[ x0 ][ y0 ])

Proposed spec change:

if( Min( lfnstWidth, lfnstHeight ) >= 4 && sps_lfnst_enabled_flag = = 1 &&

CuPredMode[ chType ][ x0 ][ y0 ] = = MODE_INTRA &&
IntraSubPartitionsSplitType = = ISP_NO_SPLIT &&
( !intra_mip_flag[ x0 ][ y0 ] \|\| Min( lfnstWidth, lfnstHeight ) >= 16 )
&&
(tu_mts_idx[ x0 ][ y0 ] == 0 \|\| !tu_cbf_luma[ x0 ][ y0 ]) &&
Max( cbWidth, cbHeight ) <= MaxTbSizeY) {

[bbross]

This is fixed by the adoption of JVET-P1026 where the mts_idx now depends on the lfnst_idx.