Vehicle may not breach fence again after entering RETURN_PATH

[peterbarker]

Bug report

Issue details

Similarly to the PR fixing "in_landing_sequence" (DO_LAND_START) (#29730), we probably have a bug where we won't breach a fence for a second time if we have entered a return path.

Version
master and 4.6 at least

Platform
[ X ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

Airframe type
All

Hardware type
All (reproducible in SITL)