ffmpeg: minor simplification of wraping code

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

ffmpeg.c

@@ -2774,8 +2774,8 @@ static int process_input(int file_index)
                av_ts2timestr(input_files[ist->file_index]->ts_offset, &AV_TIME_BASE_Q));
     }
 
-    if(!ist->wrap_correction_done && input_files[file_index]->ctx->start_time != AV_NOPTS_VALUE && ist->st->pts_wrap_bits < 64){
-        int64_t stime = av_rescale_q(input_files[file_index]->ctx->start_time, AV_TIME_BASE_Q, ist->st->time_base);
+    if(!ist->wrap_correction_done && is->start_time != AV_NOPTS_VALUE && ist->st->pts_wrap_bits < 64){
+        int64_t stime = av_rescale_q(is->start_time, AV_TIME_BASE_Q, ist->st->time_base);
         int64_t stime2= stime + (1ULL<<ist->st->pts_wrap_bits);
         ist->wrap_correction_done = 1;