message: fix crash with --enable-approx-int2ptr
diff: @@ -1991,7 +1991,7 @@ expr Memory::int2ptr(const expr &val) const {
  assert(!memory_unused() && observesAddresses());
  // TODO: missing pointer escaping
  if (config::enable_approx_int2ptr) {
  - DisjointExpr<expr> ret;
  + DisjointExpr<expr> ret(expr{});
  ret.add(Pointer::mkNullPointer(*this).release(), val == 0);
  auto add = [&](unsigned limit, bool local) {
  