Fix command line parsing in media player sample.

Fix command line parsing in media player sample.

It was broken since the addition of the call to wxApp::OnInit() to
wxMediaPlayerApp::OnInit() -- as the base class parses the command line
itself, we need to use OnInitCmdLine() and OnCmdLineParsed() instead of doing
it manually if we call it.

Also don't load the play list saved in wxConfig if any command line parameters
were given as otherwise the saved files would be used first (this seems to
have been always broken...).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71926 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775