message: highgui(gtk): fix initialization order of global objects
diff: @@ -2331,6 +2331,11 @@ public:
  class GTKBackendUI : public UIBackend
  {
  public:
  + GTKBackendUI()
  + {
  + // NB: avoid static initialization order fiasco
  + (void)getGTKWindows();
  + }
  ~GTKBackendUI() CV_OVERRIDE
  {
  destroyAllWindows();
  