sbrdsp_fixed: assert that input values are in the valid range

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavcodec/sbrdsp_fixed.c

@@ -38,9 +38,14 @@ static SoftFloat sbr_sum_square_c(int (*x)[2], int n)
     int i, nz, round;
 
     for (i = 0; i < n; i += 2) {
+        // Larger values are inavlid and could cause overflows of accu.
+        av_assert2(FFABS(x[i + 0][0]) >> 29 == 0);
         accu += (int64_t)x[i + 0][0] * x[i + 0][0];
+        av_assert2(FFABS(x[i + 0][1]) >> 29 == 0);
         accu += (int64_t)x[i + 0][1] * x[i + 0][1];
+        av_assert2(FFABS(x[i + 1][0]) >> 29 == 0);
         accu += (int64_t)x[i + 1][0] * x[i + 1][0];
+        av_assert2(FFABS(x[i + 1][1]) >> 29 == 0);
         accu += (int64_t)x[i + 1][1] * x[i + 1][1];
     }