[processing] fix folding in the model

Earlier commit broke the update of lines when folding  parameters in the
modeler. This one fixes it again.

python/plugins/processing/modeler/ModelerGraphicItem.py

@@ -100,11 +100,15 @@ class ModelerGraphicItem(QGraphicsItem):
             pt = self.getLinkPointForOutput(-1)
             pt = QPointF(0, pt.y())
             self.outButton.position = pt
+        for arrow in self.arrows:
+            arrow.updatePath()
         self.update()
 
     def foldOutput(self, folded):
         self.element.outputsFolded = folded
         self.prepareGeometryChange()
+        for arrow in self.arrows:
+            arrow.updatePath()
         self.update()
 
     def addArrow(self, arrow):