ffmpeg: check debug scanf() return value.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -2575,7 +2575,8 @@ static int transcode(OutputFile *output_files, int nb_output_files,
                     while(debug & (FF_DEBUG_DCT_COEFF|FF_DEBUG_VIS_QP|FF_DEBUG_VIS_MB_TYPE)) //unsupported, would just crash
                         debug += debug;
                 }else
-                    scanf("%d", &debug);
+                    if(scanf("%d", &debug)!=1)
+                        fprintf(stderr,"error parsing debug value\n");
                 for(i=0;i<nb_input_streams;i++) {
                     input_streams[i].st->codec->debug = debug;
                 }