`std::string` exception thrown under WSL (and possible linux)

`error: basic_string: construction from null is not valid`

### minimal example:
```cxx
#include <indicators/indicators.hpp>

using namespace indicators;

auto main() -> int {
  ProgressBar bar{};
  bar.set_progress(10);
}
```

```
Linux pc 6.6.87.2-microsoft-standard-WSL2 #1 SMP PREEMPT_DYNAMIC Thu Jun  5 18:30:46 UTC 2025 x86_64 GNU/Linux
```