avformat/aiffdec: Check size before subtraction in get_aiff_header()

Fixes: Infinite loop
Fixes: 27235/clusterfuzz-testcase-minimized-ffmpeg_dem_AIFF_fuzzer-5761398380167168

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

libavformat/aiffdec.c

@@ -120,6 +120,8 @@ static int get_aiff_header(AVFormatContext *s, int size,
     else
         sample_rate = (val + (1ULL<<(-exp-1))) >> -exp;
     par->sample_rate = sample_rate;
+    if (size < 18)
+        return AVERROR_INVALIDDATA;
     size -= 18;
 
     /* get codec id for AIFF-C */