Initialize *srcContext, *dstContext, *outContext to NULL, avoids the warnings:
libswscale/swscale-example.c:60: warning: 'outContext' may be used uninitialized in this function
libswscale/swscale-example.c:60: warning: 'dstContext' may be used uninitialized in this function
libswscale/swscale-example.c:60: warning: 'srcContext' may be used uninitialized in this function

Originally committed as revision 29008 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale
