HEAL can infinite loop: if the HEAL.APPROACHING:MoveTo call fails, the unit will fallback to FINDINGNEWTARGET, which looks for new targets to heal, which can loop around.
In #6106, the cause was that the target was not visible despite the order being given (presumably a rangemanager/los incompatbility issue).
When MoveTo() fails, the general behaviour is to finish order, since it's generally irrecoverable. This fixes the infinite loop.
Reported by: moiman