qt_intersect_spans needs Q_ASSERT

In the file qpaintengine_raster.cpp qt_intersect_spans assumes that rects is never empty. Shouldn't this have a Q_ASSERT() to check this?

static int qt_intersect_spans(QT_FT_Span *spans, int numSpans,
int *currSpan,
QT_FT_Span *outSpans, int maxOut,
const QRegion &clip)
{
const QVector<QRect> rects = clip.rects();
const int numRects = rects.size();

int r = 0;
short miny, minx, maxx, maxy;
{
const QRect &rect = rects[0];