avformat/asfdec_f: Use 64bit for packet start time

Fixes: signed integer overflow: 2147483647 + 32 cannot be represented in type 'int'
Fixes: 49014/clusterfuzz-testcase-minimized-ffmpeg_dem_ASF_fuzzer-6314973315334144

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

libavformat/asfdec_f.c

@@ -104,7 +104,7 @@ typedef struct ASFContext {
     int ts_is_pts;
     int packet_multi_size;
     int packet_time_delta;
-    int packet_time_start;
+    int64_t packet_time_start;
     int64_t packet_pos;
 
     int stream_index;