Check param in sws_getCachedContext().
Patch by KO Myung-Hun komh chollian net
Original thread: [FFmpeg-devel] [PATCH] param check in sws_getCachedContext()
Date: Wed Jan 9 11:15:19 CET 2008

Originally committed as revision 25775 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale
