Use integer division in DockSplitter.draw

[greschd]

Tiny fix: use integer division in calls to wx.DC.DrawLine in the DockSplitter.draw method.

Trying to run with wxPython==4.2.0 (Python 3.10, Linux+Windows), this caused the following error:

Traceback (most recent call last):
  File "<venv>/python/lib/python3.10/site-packages/pyface/dock/dock_window.py", line 494, in _paint
    sizer.Draw(self.control)
  File "<venv>/python/lib/python3.10/site-packages/pyface/dock/dock_sizer.py", line 4233, in Draw
    self._contents.draw(set_standard_font(wx.PaintDC(window)))
  File "<venv>/python/lib/python3.10/site-packages/pyface/dock/dock_sizer.py", line 3510, in draw
    item.draw(dc)
  File "<venv>/python/lib/python3.10/site-packages/pyface/dock/dock_sizer.py", line 3514, in draw
    item.draw(dc)
  File "<venv>/python/lib/python3.10/site-packages/pyface/dock/dock_sizer.py", line 1317, in draw
    dc.DrawLine(x + idx + 1, y + dy / 2, x + dx - 2, y + dy / 2)
TypeError: DC.DrawLine(): arguments did not match any overloaded call:
  overload 1: argument 2 has unexpected type 'float'
  overload 2: argument 1 has unexpected type 'int'

Related: #1187

[corranwebster]

Thanks for the contribution! We haven't had the resources for bringing things up to date with WxPython beyond 4.0, so any further fixes (or even simply reports) of issues that you've run into would be much appreciated.

The fix itself looks good, so assuming tests pass, I'll merge it later today. It might be a couple of months before the next release, however.

[corranwebster]

Looks like the copyright date check failed with the new year - not your problem, but this may have to wait until we get that resolved.

[greschd]

Great, thanks for taking the time to review!

[corranwebster]

Style failures are fixed in #1191, otherwise this is good.