exit with error code if av_encode failed

Originally committed as revision 16704 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -3918,8 +3918,9 @@ int main(int argc, char **argv)
     }
 
     ti = getutime();
-    av_encode(output_files, nb_output_files, input_files, nb_input_files,
-              stream_maps, nb_stream_maps);
+    if (av_encode(output_files, nb_output_files, input_files, nb_input_files,
+                  stream_maps, nb_stream_maps) < 0)
+        av_exit(1);
     ti = getutime() - ti;
     if (do_benchmark) {
         printf("bench: utime=%0.3fs\n", ti / 1000000.0);