[BUG] Parens disappear in `std::cout` expressions

Parens are not preserved in one of the regression-tests: `mixed-test-parens.cpp2`

The code
```cpp
std::cout << (1+2)*(3+v[0]);
```
is compiled by the cppfront to:
```cpp
std::cout << (1+2)* 3 + v[0];
```
