Fixed a clear case of brain failure (Don't try to show graphFrame window if MPL isn't installed)

gui/mainFrame.py

@@ -392,12 +392,10 @@ class MainFrame(wx.Frame):
         self.waitDialog.Destroy()
 
     def openGraphFrame(self, event):
-        if not gui.graphFrame.enabled:
-            return
-
         if not self.graphFrame:
             self.graphFrame = GraphFrame(self)
-            self.graphFrame.Show()
+            if gui.graphFrame.enabled:
+                self.graphFrame.Show()
         else:
             self.graphFrame.SetFocus()