PlanManager: prevent memory leak when writing mission items to vehicle

[AsensioL]

Prevent MissionIteam leakage when uploading mission to vehicle

Description

When uploading a mission to a vehicle, the MissionController takes its VisualMissionItems and copies them into a temporary QList<MissionItem*>.

Detailed explanation:

1. This starts at MissionController::sendToVehicle, which calls MissionController::sendItemsToVehicle where MissionItems are allocated by ...
2. calling MissionController::_convertToMissionItems, which itself ...
3. defers to the pure virtual function VisualMissionItem::appendMissionItems, where the implementation depends on the type of VisualMissionItem, but they all
4. use new, and set the VisualMissionItem's parent to the Vehicle* instance.

When the connected vehicle is one that skips the first MissionItem (see implementation of PlanManager::writeMissionItems) then, the first MissionItem* is never moved to the PlanManager::_writeMissionItems and is leaked until the Vehicle* instance is destroyed (which kicks in Qt's cleaning broom).

Checklist:

• Review Contribution Guidelines.
• Review Code of Conduct.
• I have tested my changes.

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[DonLakeFlyer]

Yup, thanks for the fix.