avcodec/tests/jpeg2000dwt: Use 64bit in err2 computation

This issue cannot happen with the current function parameters

Fixes: CID1500309 Unintentional integer overflow

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/tests/jpeg2000dwt.c

@@ -57,7 +57,7 @@ static int test_dwt(int *array, int *ref, int border[2][2], int decomp_levels, i
                     j, array[j], ref[j],decomp_levels, border[0][0], border[0][1], border[1][0], border[1][1]);
             return 2;
         }
-        err2 += (array[j] - ref[j]) * (array[j] - ref[j]);
+        err2 += (array[j] - ref[j]) * (int64_t)(array[j] - ref[j]);
         array[j] = ref[j];
     }
     ff_dwt_destroy(s);