What was fixed
[CompletionData.cpp](cci:7://file:///c:/Users/T2430514/Downloads/winget-cli/src/AppInstallerCLICore/CompletionData.cpp:0:0-0:0) passed a potentially negative `char` to `std::isspace`, invoking undefined behaviour on non-ASCII input (signed `char` platforms). This occasionally caused crashes or incorrect cursor repositioning when autocompleting commands containing UTF-8 characters.

### How it was fixed
The character is now explicitly cast to `unsigned char` before the `std::isspace` check:

```cpp
!std::isspace(static_cast<unsigned char>(commandLine[cursor - 1]))
```

This aligns with standard C++ guidance and makes the completion logic robust across all locales.

Co-Authored-By: S. M. Mohiuddin Khan Shiam <147746955+mohiuddin-khan-shiam@users.noreply.github.com>

### What was fixed
[CompletionData.cpp](cci:7://file:///c:/Users/T2430514/Downloads/winget-cli/src/AppInstallerCLICore/CompletionData.cpp:0:0-0:0) passed a potentially negative `char` to `std::isspace`, invoking undefined behaviour on non-ASCII input (signed `char` platforms). This occasionally caused crashes or incorrect cursor repositioning when autocompleting commands containing UTF-8 characters.

### How it was fixed
The character is now explicitly cast to `unsigned char` before the `std::isspace` check:

```cpp
!std::isspace(static_cast<unsigned char>(commandLine[cursor - 1]))
```

This aligns with standard C++ guidance and makes the completion logic robust across all locales.