Pull request type

• Code changes (bugfix, features)
• Code maintenance (refactoring, formatting, tests)
• ReadMe, Docs and GitHub updates
• Other (please describe):

Checklist

• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md has been updated (if relevant)

Current behavior

time_overshoot=None causes an error in Flight._simulate.

New behavior

Fixes #804 by setting time_overshoot to the base flight value when it is None.

Breaking change

• No

Additional information

Still need to fix time_overshoot=False problem described in #802