avformat/nutdec: fix obvious typo

Fixes #6742.

libavformat/nutdec.c

@@ -582,7 +582,7 @@ static int decode_info_header(NUTContext *nut)
             if (stream_id_plus1 && !strcmp(name, "r_frame_rate")) {
                 sscanf(str_value, "%d/%d", &st->r_frame_rate.num, &st->r_frame_rate.den);
                 if (st->r_frame_rate.num >= 1000LL*st->r_frame_rate.den ||
-                    st->r_frame_rate.num < 0 || st->r_frame_rate.num < 0)
+                    st->r_frame_rate.num < 0 || st->r_frame_rate.den < 0)
                     st->r_frame_rate.num = st->r_frame_rate.den = 0;
                 continue;
             }