FFplay : Avoid manipulating NULL data pointers so that future checks

remain valid. This fixes segfaults for those cases where data copy to
this invalid pointer is attempted.

Originally committed as revision 23264 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffplay.c

@@ -1591,7 +1591,9 @@ static int input_get_buffer(AVCodecContext *codec, AVFrame *pic)
         unsigned hshift = i == 0 ? 0 : av_pix_fmt_descriptors[ref->pic->format].log2_chroma_w;
         unsigned vshift = i == 0 ? 0 : av_pix_fmt_descriptors[ref->pic->format].log2_chroma_h;
 
+        if (ref->data[i]) {
         ref->data[i]    += (edge >> hshift) + ((edge * ref->linesize[i]) >> vshift);
+        }
         pic->data[i]     = ref->data[i];
         pic->linesize[i] = ref->linesize[i];
     }