wxGUI/menu: fix histogramming tool

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@50365 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/lmgr/frame.py

@@ -1192,9 +1192,10 @@ class GMFrame(wx.Frame):
     def OnHistogram(self, event):
         """!Init histogram display canvas and tools
         """
+        from modules.histogram import HistogramFrame
         win = HistogramFrame(self)
         
-        win.CentreOnParent()
+        win.CentreOnScreen()
         win.Show()
         win.Refresh()
         win.Update()