Ensure test only fails as originally designed

The test will otherwise exhibit undefined behaviour under CBMC 6
settings (where malloc may fail). This, in turn, can cause the expected
patterns not to show up in the trace.

Author: tautschnig

regression/cbmc/trace-values/unbounded_array.c

@@ -6,6 +6,7 @@ int main(int argc, char *argv[])
   unsigned long size;
   __CPROVER_assume(size < 100 && size > 10);
   int *array = malloc(size * sizeof(int));
+  __CPROVER_assume(array);
   array[size - 1] = 42;
   int fixed_array[] = {1, 2};
   __CPROVER_array_replace(array, fixed_array);