Merge pull request matplotlib#3995 from cgohlke/patch-1

BUG : Fix wx._core.PyAssertionError ... wxGetStockLabel(): invalid stock item ID

Author: tacaswell

examples/user_interfaces/mathtext_wx.py

@@ -65,7 +65,7 @@ def __init__(self, parent, title):
             menu = wx.Menu()
             for i, (mt, func) in enumerate(functions):
                 bm = mathtext_to_wxbitmap(mt)
-                item = wx.MenuItem(menu, 1000 + i, "")
+                item = wx.MenuItem(menu, 1000 + i, " ")
                 item.SetBitmap(bm)
                 menu.AppendItem(item)
                 self.Bind(wx.EVT_MENU, self.OnChangePlot, item)