Pull request type

• Code changes (bugfix, features)

Checklist

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest --runslow) have passed locally

Current behavior

• I'm getting an error when initializing a flight object using a motor that has an burn_out_time lower than the initial time step.
• The error happens when trying to access the max acceleration during the burn time
• This is particularly common for deployable or multi-stage flight simulations.
• ValueError: attempt to get argmax of an empty sequence

New behavior

A simple code line solved the problem, and I added a simple test to avoid getting this problem again.

Breaking change

• No

Additional information

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