Player hangs if simulation is paused, and then while in the paused state, the simulation is stopped

[sminsuk]

Describe the bug
After a simulation has been run and then paused, stopping the simulation hangs the player. The stop button stays in its "depressed" appearance, the Mac's "spinning beach ball of death" appears, and the player becomes unresponsive. Mac's Force Quit dialog shows "python (not responding)". The only way to recover is to Force Quit, and restart the player. I have only noticed this with my hackathon project, but I have no reason to suspect that the content of the simulation matters.

[Edit: Actually, the content of the simulation does appear to matter. My simulation uses AdhesionFlex, and I noticed that Issue #35 has something to do with AdhesionFlex, though I don't understand what's being described there. So I tried it with a different simulation without AdhesionFlex, and I did not have the same problem. So these two issues may be related.]

To Reproduce
Steps to reproduce the behavior:

1. Run a simulation [Edit: the simulation probably must use AdhesionFlex.]
2. Click the Pause button (or the Step button)
3. Click the Stop button.
4. See error

If after pausing, you click the "Run" button to continue execution, Stop then works correctly. The hang occurs only when you are in the paused state.

Expected behavior
The Stop button should cause the simulation execution to stop properly (and not hang the player).

Screenshots
Stop button frozen in depressed position:

Terminal window while simulation paused:

Terminal window after clicking Stop:

Desktop(please complete the following information):

• Device: MacBook Pro
• Processor: Apple M1 Pro
• OS: macOS Monterey
• CompuCell3D Version and commit tag :
  Version: 4.6.0 Revision: 2
  Commit Tag: 397f8b1
• How did you install the code : binary installer
• File name of the installer used to install CC3D
  I believe: cc3d-installer-osx-4.6.0-arm64.sh