Summary

The two streaming ZIP writer paths returned MZ_FALSE when their final data descriptor write was short, but left mz_zip_get_last_error() at MZ_ZIP_NO_ERROR. Callers therefore received a failure result without a useful error code.

Set MZ_ZIP_FILE_WRITE_FAILED in both the memory-input and read-callback writer paths, matching the surrounding archive write checks.

Testing

• Added a short-write callback regression covering mz_zip_writer_add_mem() and mz_zip_writer_add_read_buf_callback().
• Against unmodified 77d0dce, both sections fail because the error remains 0 instead of MZ_ZIP_FILE_WRITE_FAILED (exit 2).
• With this change, the focused test passes all 10 assertions.
• Full CMake/Ninja build completed and ctest --output-on-failure passed 100%.