message: SMT: relax sext/zext to accept 0 as arg
diff: @@ -773,8 +773,10 @@ expr expr::sgt(const expr &rhs) const {
  }
  expr expr::sext(unsigned amount) const {
  - assert(amount > 0);
  C();
  + if (amount == 0)
  + return *this;
  +
  int64_t n;
  if (isInt(n))
  return mkInt(n, bits() + amount);
  @@ -782,7 +784,9 @@ expr expr::sext(unsigned amount) const {
  }
  expr expr::zext(unsigned amount) const {
  - assert(amount > 0);
  + if (amount == 0)
  + return *this;
  +
  uint64_t n;
  if (isUInt(n))
  return mkUInt(n, bits() + amount);
  