Enable mouse tracking in wxQT, thanks @seandepagnier

This is needed so qt mouse events are triggered without a button pressed.
Note that I modified this to prevent a crash if m_qtWindow was null (reproducible with controls sample and the original patch from Sean)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77925 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/qt/window.cpp

@@ -220,6 +220,8 @@ bool wxWindowQt::Create( wxWindowQt * parent, wxWindowID id, const wxPoint & pos
         {
             m_qtWindow = new wxQtWidget( parent, this );
         }
+
+        GetHandle()->setMouseTracking(true);
     }
 
     if ( !wxWindowBase::CreateBase( parent, id, pos, size, style, wxDefaultValidator, name ))