OK, let's see, as far as I could understand, getFlxFrameBitmapData() should
return the bitmapdata of the actual frame even if it is flipped. It should
load the bitmapdata once and return that bitmapdata  each time is called.

framePixels is null because it's not really used for drawing on CPP/neko.
The only way I found to initialize framePixels was calling drawFrame() each
time so it could get the updated animation frame. If calling each time
drawFrame() is better or not I don't really know that's why I asked for the
gurus XD