Monitoring ends after a random amount of time

[Adreitz]

This is a second issue I noticed after a few tests of memplot. I initially specified the length of time I expected Python to take to generate an image at my target resolution (~1000s). Memplot ran for about six seconds and then stopped. I thought maybe I had specified too long of a time, so I tried it again with -dur 0. This time it ran for about 220 seconds and then stopped again. Python was still running with the same PID, so I just restarted memplot. I had to run it manually four more times, when it stopped at ~550, 27, and 64 seconds (the last run ended as expected when I terminated python).

MacBook Pro M2 Max 64GB MacOS 13.4b2