BaseRender: Allow 1px wrong in aspect ratio to not do completeley refit the image

This fixes off by 1 errors when running on systems with broken pixel Ratio.

Basically with a pixel Ratio of: 1.000512 as seen here: http://forum.kodi.tv/showthread.php?tid=210815 You end up with 1919 pixels instead of 1920 pixels. This patch prefers to better have 1 px wrong in ratio than using a scaler to resort all the pixels.