avformat/aaxdec: Check that segments table has been initialized

Fixes: Timeout
Fixes: 29766/clusterfuzz-testcase-minimized-ffmpeg_dem_AAX_fuzzer-5635887566290944

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

libavformat/aaxdec.c

@@ -264,6 +264,11 @@ static int aax_read_header(AVFormatContext *s)
         }
     }
 
+    if (!a->segments[0].end) {
+        ret = AVERROR_INVALIDDATA;
+        goto fail;
+    }
+
     st = avformat_new_stream(s, NULL);
     if (!st) {
         ret = AVERROR(ENOMEM);