ofVideoPlayer.getCurrentFrame() is not working properly

OS : arch linux
OF version : 0.11.0

first, `ofVideoPlayer.getPosition()` is not working.

`getCurrentFrame()` and `getTotalFrames()` also possible.
but I found that `getCurrentFrame()` is working properly after call `getDuration()`

I'm not sure this is happen on other OS. currently happen on linux (`ofGstVideoPlayer`)