ffmpeg_opt: Dont exit on avformat_find_stream_info() failure if there are streams

This allows "-codec copy -f framecrc" on files with only unindentifyable streams
Reviewed-by: Stefano Sabatini <stefasab@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg_opt.c

@@ -888,9 +888,11 @@ static int open_input_file(OptionsContext *o, const char *filename)
     ret = avformat_find_stream_info(ic, opts);
     if (ret < 0) {
         av_log(NULL, AV_LOG_FATAL, "%s: could not find codec parameters\n", filename);
+        if (ic->nb_streams == 0) {
             avformat_close_input(&ic);
             exit_program(1);
         }
+    }
 
     timestamp = (o->start_time == AV_NOPTS_VALUE) ? 0 : o->start_time;
     /* add the stream start time */