Codechange: be consistent in what CheckPaletteAnim() does and when it is called

Additionally, make sure this is a class method. Later commits
will make use of this.

src/video/win32_v.cpp

@@ -1201,7 +1201,6 @@ void VideoDriver_Win32::MainLoop()
 
 	_wnd.running = true;
 
-	CheckPaletteAnim();
 	for (;;) {
 		InteractiveRandom(); // randomness