avformat/sbgdec: clamp end_ts

Fixes: signed integer overflow: 9223372036851135042 + 15666854 cannot be represented in type 'long'
Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_dem_SBG_fuzzer-6573717339111424

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/sbgdec.c

@@ -1478,7 +1478,7 @@ static int sbg_read_packet(AVFormatContext *avf, AVPacket *packet)
     int ret;
 
     ts = ffstream(avf->streams[0])->cur_dts;
-    end_ts = ts + avf->streams[0]->codecpar->frame_size;
+    end_ts = av_sat_add64(ts, avf->streams[0]->codecpar->frame_size);
     if (avf->streams[0]->duration != AV_NOPTS_VALUE)
         end_ts = FFMIN(avf->streams[0]->start_time + avf->streams[0]->duration,
                        end_ts);