Masked controls modules and demos need Py3-related fixes

[RobinD42]

[esitarski]

How is this going?
The masked control demo seem to work on Windows, but it is easy to mess up the formats and to get errors on Ubuntu. Just enter valid characters, then go back and type in invalid chars.

---

File "/home/esitarski/.local/lib/python3.5/site-packages/wx/lib/masked/maskededit.py", line 2703, in _configure
self._calcTemplate(reset_fillchar, reset_default)
File "/home/esitarski/.local/lib/python3.5/site-packages/wx/lib/masked/maskededit.py", line 2506, in _calcTemplate
if curvalue[pos] == old_fillchars[pos] and old_fillchars[pos] != fillChar:
IndexError: list index out of range
esitarski@esitarski-XPS-13-9370:~/Projects/wxPython-demo-4.0.7/demo$ p3 MaskedEditControls.py
Python 3.5.2 (default, Oct 8 2019, 13:06:37)
[GCC 5.4.0 20160609]
wx.version: 4.0.4 gtk3 (phoenix) wxWidgets 3.0.5
Traceback (most recent call last):
File "/home/esitarski/.local/lib/python3.5/site-packages/wx/core.py", line 3259, in
lambda event: event.callable(*event.args, **event.kw) )
File "/home/esitarski/.local/lib/python3.5/site-packages/wx/lib/masked/maskededit.py", line 5649, in _fixSelection
elif sel_start > self._goEnd(getPosOnly=True):
File "/home/esitarski/.local/lib/python3.5/site-packages/wx/lib/masked/maskededit.py", line 4589, in _goEnd
char = text[i]
IndexError: string index out of range

[RobinD42]

If you're able to fix some of the issues you run into then PRs are welcome. I don't use the masked controls myself so they do not get much of my attention.