Catch 'clipboard already open' errors in editors

Apparently following commits have not fixed the problem completely,
because it still happens (although not so often).

changeset: 2019:b8f795bdfe9f
user: Andrey Skvortsov <andrej.skvortzov@gmail.com>
date: Fri May 25 17:40:29 2018 +0300
summary: fix hangs on mouse selection in case if wxPython uses wxWidgets with GTK3+ support

changeset: 2018:5ce6d08ff2c7
user: Andrey Skvortsov <andrej.skvortzov@gmail.com>
date: Fri May 25 17:23:15 2018 +0300
summary: make clipboard open minimal time as wxPython documentation recommends

<?xml version="1.0" encoding="ISO-8859-1" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <xsd:element name="Python">
    <xsd:complexType>
      <xsd:annotation>
        <xsd:documentation>Formatted text according to parts of XHTML 1.1</xsd:documentation>
      </xsd:annotation>
      <xsd:sequence>
        <xsd:any namespace="http://www.w3.org/1999/xhtml" processContents="lax"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>
</xsd:schema>