Fix build error by replacing stbi_write_png_to_mem with `stbi_write…

[pedroac]

…_png_to_func`

[what-the-diff]

PR Summary

• Changed How Image Data is Stored
  Instead of using a raw pointer – an older method of memory storage – we have switched to using a std::vector<unsigned char>. This software object simplifies memory handling, reducing the risk of programming errors that could cause the software to crash.

• Added a New Function to Write Image Data
  This update introduces a new function, write_to_vec, that adds image data directly into our storage vector.

• Corrected Size Calculation for Data Storage
  Previously, the parameter for the archive_entry_set_size function used the size of the old raw pointer. Now, it accurately uses the size of our image storage vector, refining how we track how much memory we're using.

• Adjusted How Data is Written
  Finally, we have altered the archive_write_data function, which is responsible for recording our image data. Instead of writing from the old data handling method, it now writes from our newly implemented vector. This ensures any data writing will accurately reflect our upgraded storage method.

[gemini-code-assist]

Code Review

This pull request refactors the PNG encoding logic in SpriteUnpacker to use stbi_write_png_to_func with a std::vector instead of stbi_write_png_to_mem with a raw buffer, which improves memory management and idiomatic C++ usage. A review comment suggests adding a safety check for the size parameter in the write callback to ensure robustness against invalid inputs during vector insertion.

[gemini-code-assist]

The stbi_write_png_to_func callback receives size as an int. While it's unlikely to be negative in a successful scenario, adding a check to handle non-positive size values would make the callback more robust and prevent potential undefined behavior from std::vector::insert if an invalid size is ever passed.

        auto write_to_vec = [](void* context, void* data, int size) {
            if (size <= 0) {
                return;
            }
            auto* vec = static_cast<std::vector<unsigned char>*>(context);
            const auto* bytes = static_cast<const unsigned char*>(data);
            vec->insert(vec->end(), bytes, bytes + size);
        };