app: in bucket-fill tool, cancel async on tool destruction
When computing line-art, don't ref the bucket-fill tool in the async data, and rather cancel any ongoing async upon tool destruction, so that the async callback doesn't attept to touch the now-dead tool. This avoids segfaulting in the async callback when switching to a different tool, while a line-art async operation is active. Additionally, always cancel any previous async operation in gimp_bucket_fill_compute_line_art(), even if not starting a new one.
Showing with 20 additions and 11 deletions