bpo-33110: Catch errors raised when running add_done_callback on already completed...

bpo-33110: Catch errors raised when running add_done_callback on already completed futures (GH-13141)

Wrap the callback call within the `add_done_callback` function within concurrent.futures, in order to behave in an identical manner to callbacks added to a running future are triggered once it has completed.
(cherry picked from commit 2a3a2ece502c05ea33c95dd0db497189e0354bfd)

Co-authored-by: Sam Martin <ABitMoreDepth@users.noreply.github.com>