fish will print messages for some jobs when they exit abnormally, such as
with SIGABRT. If a job exits abnormally inside the prompt, then (prior to
this commit) fish would print the message and re-trigger the prompt, which
could result in an infinite loop. This has existed for a very long time.
Fix it by reaping jobs after running the prompt, and NOT triggering a
redraw based on that reaping. We still print the message but the prompt is
not executed.
Add a test.
Fixes#9796
