win_sparkle_update_cancelled_callback not called when closing installation window

[glaubitz]

Currently, the win_sparkle_update_cancelled_callback callback function is called when the user click "Skip Update", "Remind Me Later" or when the "Cancel" button is clicked when the update is being downloaded.

However, win_sparkle_update_cancelled_callback is not called when the user just closes the "Ready to install" dialog instead of clicking "Install updates" although this effectively cancels the update process as well.

[vslavik]

Please submit a PR with the fix, then. As one of the very few users of this callback, you’re in the best position to do it and contribute back.