[cores] RenderManager::GetStats - now returns queue and discard separately. DVDPlayer...

[cores] RenderManager::GetStats - now returns queue and discard separately. DVDPlayerVideo - ignore discard stats for dropping frame on rewind.

The main problem is:
1) The DXVA processor allows (and requires for de-interlacing) a set of past frames. This causes the bufferLevel greater than 0.
3) DVDPlayerVideo drops any frame if bufferLevel is greater than 0 on rewind, so the renderer doesn't receive any new frame which causes freezing picture when DXVA processor is used.

This changes behavior DVDPlayerVideo to do not consider the discard queue before dropping frame on rewind.