QTransform fails when using negative w in projective transforms

Consider the following function in qTransform

static inline bool lineTo_clipped(QPainterPath &path, const QTransform &transform, const QPointF &a, const QPointF &b,
bool needsMoveTo, bool needsLineTo = true)
{
QHomogeneousCoordinate ha = mapHomogeneous(transform, a);
QHomogeneousCoordinate hb = mapHomogeneous(transform, b);

if (ha.w < Q_NEAR_CLIP && hb.w < Q_NEAR_CLIP)
return false;

A valid projective transform may have ha.w be -0.997. This code and many other checks like it assume that w > 0.