Handle loss of position during backtransition

[RomanBapst]

Solved Problem

When the estimator declares local position invalid during a VTOL backtransition in an autonomous mode, the vehicle enters a fixed bank loiter. This is not desired during a backtransition, as the vehicle will start to turn.

Solution

Explicitly handle the case where we don't control position during the backtransition by setting the roll setpoint to zero.

Changelog Entry

For release notes:

Bugfix: Prevent fixed bank loiter during backtransition when we lose local position.

Alternatives

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Test coverage

• Unit/integration test: ...
• Simulation/hardware testing logs: https://review.px4.io/

Context

Related links, screenshot before/after, video