avcodec/apedec: Check length in long_filter_high_3800()

Fixes out of array read
Fixes: 0a7ff0c1d93da9cef28a315ec91b692a/asan_heap-oob_4a52e5_3604_9c56dbb20e308f4faeef7b35f688521a.ape

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit cd7524fd)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/apedec.c

@@ -905,6 +905,9 @@ static void long_filter_high_3800(int32_t *buffer, int order, int shift,
     int i, j;
     int32_t dotprod, sign;
 
+    if (order >= length)
+        return;
+
     memset(coeffs, 0, order * sizeof(*coeffs));
     for (i = 0; i < order; i++)
         delay[i] = buffer[i];