pudb3 crashes when you enter and quit ipdb in post-mortem mode

Just run a script, click on 'Examine' and enter post-mortem mode. Enter iPython using !. One you are in iPython quit it using Ctrl-D , it will show a list index out of range error. You can make it work with a try except, however can this be handled more correctly?

Reproduce the crash by running a script, selecting “Examine,” entering post-mortem mode, using “!” to enter iPython, and quitting with Ctrl-D. Trace the post-mortem debugger’s handling of the iPython exit and the resulting list-index error; done means quitting returns cleanly without the exception.

Written by the indexing model from the issue text.