Fix demo shebang.  Closes #15503

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxPython/trunk@77973 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Only use CallOnInit the first time a wx.App is created

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxPython/trunk@77974 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775