Update packet list on absorption in MC

[ffoucart]

Proposed changes

Fix number of packets in packet list after an absorption event.

Upgrade instructions

NA

Code review checklist

• [ ] The code is documented and the documentation renders correctly. Run make doc to generate the documentation locally into BUILD_DIR/docs/html. Then open index.html.
• [ ] The code follows the stylistic and code quality guidelines listed in the code review guide.
• [ ] The PR lists upgrade instructions and is labeled bugfix or new feature if appropriate.

[ffoucart]

@nilsdeppe @kidder Another small bugfix...