added wxString::operator[](int) as it's commonly used in code working with file/stream read functions which have int return value

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45100 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/string.h

@@ -1839,6 +1839,7 @@ public:
   wxString& operator+=(wxUniChar ch)
     { m_impl += EncodeChar(ch); return *this; }
   wxString& operator+=(wxUniCharRef ch) { return *this += wxUniChar(ch); }
+  wxString& operator+=(int ch) { return *this += wxUniChar(ch); }
   wxString& operator+=(char ch) { return *this += wxUniChar(ch); }
   wxString& operator+=(unsigned char ch) { return *this += wxUniChar(ch); }
   wxString& operator+=(wchar_t ch) { return *this += wxUniChar(ch); }