Fixes: assert in QPainter::fillRect on very large paint devices

For devices taller than 32768, fillRect with linear gradient would
go below the cliprect.

Task-number: QTBUG-26766
Change-Id: I516ede1545909e9ce2de5812c61bb473f99f5759
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/gui/painting/qrasterizer.cpp

@@ -891,6 +891,8 @@ void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width,
                 const Q16Dot16 rowHeight = qMin(yFP + Q16Dot16Factor, yPb)
                                            - qMax(yFP, yPa);
                 const int y = Q16Dot16ToInt(yFP);
+                if (y > d->clipRect.bottom())
+                    break;
                 for (int i = 0; i < n; ++i) {
                     buffer.addSpan(x[i], len[i], y,
                                    Q16Dot16ToInt(Q16Dot16Multiply(rowHeight, coverage[i])));