Move clearhilight() call to gviz.setlayer()

Calling clearhilight directly was probably leading to some exceptions
hidden by an try: except: pass block

printrun/gviz.py

@@ -254,6 +254,7 @@ class Gviz(wx.Panel):
 
     def setlayer(self, layer):
         if layer in self.layers:
+            self.clearhilights()
             self.layerindex = self.layers[layer]
             self.dirty = 1
             self.showall = 0

printrun/pronterface.py

@@ -446,7 +446,6 @@ class PronterWindow(MainWindow, pronsole.pronsole):
         layerz = self.fgcode.all_layers[newlayer].z
         if layerz is not None:
             self.curlayer = layerz
-        wx.CallAfter(self.gviz.clearhilights)
         wx.CallAfter(self.gviz.setlayer, newlayer)
 
     def do_pront_extrude(self, l = ""):