AVFilterBuffereRef in avfilter_default_get_video_buffer().

The error was being caused by the previous patch which resized
AVFilterBuffer's data and linesize arrays to 8.

Patch by S.N. Hemanth Meenakshisundaram" &smeenaks&ucsd&edu&.

Originally committed as revision 24727 to svn://svn.ffmpeg.org/ffmpeg/trunk