avformat/samidec: Sanity check pts

Fixes: signed integer overflow: 0 - -9223372036854775808 cannot be represented in type 'long'
Fixes: 29743/clusterfuzz-testcase-minimized-ffmpeg_dem_SAMI_fuzzer-5499256859394048

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

libavformat/samidec.c

@@ -95,6 +95,11 @@ static int sami_read_header(AVFormatContext *s)
                 const char *p = ff_smil_get_attr_ptr(buf.str, "Start");
                 sub->pos      = pos;
                 sub->pts      = p ? strtol(p, NULL, 10) : 0;
+                if (sub->pts <= INT64_MIN/2 || sub->pts >= INT64_MAX/2) {
+                    res = AVERROR_PATCHWELCOME;
+                    goto end;
+                }
+
                 sub->duration = -1;
             }
         }