avcodec/adpcm: Check input buffer size

Larger values will lead to integer overflows in intermediates
No testcase

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5f84a7263e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/adpcm.c

@@ -735,6 +735,8 @@ static int get_nb_samples(AVCodecContext *avctx, GetByteContext *gb,
 
     if(ch <= 0)
         return 0;
+    if (buf_size > INT_MAX / 2)
+        return 0;
 
     switch (avctx->codec->id) {
     /* constant, only check buf_size */