Fence_action parameter set to 0 when clearing a fence

#### Issue details
The parameter fence_action is automatically set to 0 the fence is cleared (right click in Plan page ---> geofence ----> clear)

#### Version
Mission planner 1.3.73 and Plane 4.0.6

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ x] Plane
[ ] Rover
[ ] Sub

#### Airframe type
Tiltrotor

#### Hardware type
Black cube

#### Logs
_Please provide a link to any relevant logs that show the issue_

Reproduce the issue in Mission Planner by opening the Plan page, right-clicking the geofence, and selecting clear with a Plane vehicle. Trace where the fence_action parameter is handled during this operation; done means the parameter no longer changes unexpectedly when the fence is cleared, with the expected behavior confirmed against the issue context.

Written by the indexing model from the issue text.