When non-table value is passed to the `operator<<`, it assumes that the
original C++ code looks like the following.
```cpp
std::cout << "key = " << v << std::endl;
```
In this case, the comment associated to `v` should be put just after
`v`, not before.
```toml
key = # comment <= bad
"value"
key = "value" # comment <= good
```
So, if `v` is not a table it would put comments just after the value.