Incorrect scaling operation in triangle list derivation

[rlliao]

In UnitTool.cpp PU::getTriangleMergeCandidates, the scaling process in averaging L0 and L1 motion vectors of a bi-prediction candidate is incorrect. When the reference picture of L1 mv is the same as L0 motion vector, scaling is still applied to L1 mv. Specifically:

aveMv = aveMv.scaleMv( xGetDistScaleFactor( curPicPoc, refPicPocL0, curPicPoc, refPicPocL1 ) );

Should be:

int32_t distscale = xGetDistScaleFactor( curPicPoc, refPicPocL0,
curPicPoc, refPicPocL1 );
if( distscale != 4096 )
{

aveMv = aveMv.scaleMv( distscale );

}

[XiangLi]

Fixed in ​https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/merge_requests/130.