avformat/smacker: Check for too small pts_inc

Fixes: negation of -2147483648 cannot be represented in type 'int'; cast to an unsigned type to negate this value to itself
Fixes: 26910/clusterfuzz-testcase-minimized-ffmpeg_dem_SMACKER_fuzzer-6705429132476416

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

libavformat/smacker.c

@@ -105,8 +105,8 @@ static int smacker_read_header(AVFormatContext *s)
     height = avio_rl32(pb);
     smk->frames = avio_rl32(pb);
     pts_inc = avio_rl32(pb);
-    if (pts_inc > INT_MAX / 100) {
-        av_log(s, AV_LOG_ERROR, "pts_inc %d is too large\n", pts_inc);
+    if (pts_inc > INT_MAX / 100 || pts_inc == INT_MIN) {
+        av_log(s, AV_LOG_ERROR, "pts_inc %d is invalid\n", pts_inc);
         return AVERROR_INVALIDDATA;
     }