fftools/ffprobe: Avoid overflow when calculating DAR

Both the codecpar's width and height, and the SAR num and den are
ints, which can overflow. Cast to int64_t, which is what av_reduce
takes.

Without this, occasionally, display_aspect_ratio can be negative in
ffprobe's -show_stream output.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

fftools/ffprobe.c

@@ -3324,8 +3324,8 @@ static int show_stream(WriterContext *w, AVFormatContext *fmt_ctx, int stream_id
         if (sar.num) {
             print_q("sample_aspect_ratio", sar, ':');
             av_reduce(&dar.num, &dar.den,
-                      par->width  * sar.num,
-                      par->height * sar.den,
+                      (int64_t) par->width  * sar.num,
+                      (int64_t) par->height * sar.den,
                       1024*1024);
             print_q("display_aspect_ratio", dar, ':');
         } else {