make clipboard open minimal time as wxPython documentation recommends

https://wxpython.org/Phoenix/docs/html/wx.Clipboard.html#wx.Clipboard.GetData

"Call wx.Clipboard.Open to get ownership of the clipboard. If this
operation returns True, you now own the clipboard. Call
wx.Clipboard.SetData to put data on the clipboard, or
wx.Clipboard.GetData to retrieve data from the clipboard. Call
wx.Clipboard.Close to close the clipboard and relinquish ownership.
You should keep the clipboard open only momentarily."

Maybe it makes situation with pretty annoying error 'clipboard already
open' a little bit better.

traceback:
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/BeremizIDE.py", line 955, in OnSaveProjectMenu
self.RefreshAfterSave()
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/BeremizIDE.py", line 946, in RefreshAfterSave
self._Refresh(TITLE, FILEMENU, EDITMENU, PAGETITLES)
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/IDEFrame.py", line 926, in _Refresh
self.RefreshFunctions[element]()
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/BeremizIDE.py", line 766, in RefreshEditMenu
IDEFrame.RefreshEditMenu(self)
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/IDEFrame.py", line 1185, in RefreshEditMenu
if self.GetCopyBuffer() is not None:
File "/home/developer/WorkData/PLC/beremiz/avangard-beremiz-ide/src/../../beremiz/IDEFrame.py", line 956, in GetCopyBuffer
if wx.TheClipboard.Open():
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk3/wx/_misc.py", line 5793, in Open
return _misc_.Clipboard_Open(*args, **kwargs)
<class 'wx._core.PyAssertionError'>: C++ assertion "!m_open" failed at ../src/gtk/clipbrd.cpp(598) in Open(): clipboard already open

<?xml version='1.0' encoding='utf-8'?>
<PyFile xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <variables>
    <variable name="Test_Python_Var" type="INT" initial="4"/>
    <variable name="Second_Python_Var" type="INT" initial="5"/>
  </variables>
  <globals>
    <xhtml:p><![CDATA[
import time,sys,ctypes
Python_to_C_Call = PLCBinary.Python_to_C_Call
Python_to_C_Call.restype = ctypes.c_int
Python_to_C_Call.argtypes = [ctypes.c_int, ctypes.POINTER(ctypes.c_int)]

def MyPythonFunc(arg):
    i = ctypes.c_int()
    if(Python_to_C_Call(arg, i)):
        res = i.value
        print "toC:", arg, "from C:", res, "FBID:", FBID
    else:
        print "Failed Python_to_C_Call failed"
        res = None
    print "Python read PLC global :",PLCGlobals.Test_Python_Var
    PLCGlobals.Second_Python_Var = 789
    sys.stdout.flush()
    return res

async_error_test_code = """
def badaboom():
    tuple()[0]

import wx
def badaboomwx():
    wx.CallAfter(badaboom)

from threading import Timer
a = Timer(3, badaboom)
a.start()

b = Timer(6, badaboomwx)
b.start()
"""
]]></xhtml:p>
  </globals>
  <init>
    <xhtml:p><![CDATA[
global x, y
x = 2
y = 5
print "py_runtime init:", x, ",", y
]]></xhtml:p>
  </init>
  <cleanup>
    <xhtml:p><![CDATA[
print "py_runtime cleanup"
]]></xhtml:p>
  </cleanup>
  <start>
    <xhtml:p><![CDATA[
global x, y
print "py_runtime start", x * x + y * y
]]></xhtml:p>
  </start>
  <stop>
    <xhtml:p><![CDATA[
print "py_runtime stop"
]]></xhtml:p>
  </stop>
</PyFile>