Fix vehicle with AttackMove.StopWhenTargetAcquired incorrectly lost megamission in some rare situation

[TaranDahl]

Somehow, the vehicle called EnterIdleMode (probably in the functions of vehicle-related locomotors) in a move mission.
Then the megamission will be removed because the RefreshMegaMission function will only continue the megamission if the techno is in a guard mission.

[github-actions]

Nightly build for this pull request:

• compiled-dll-20f04b64feba7f79548cf23ad8ffb50f876d7ea7.zip
  These artifacts will expire in 90 days and will not be available for download after that time.

This comment is automatic and is meant to allow guests to get latest nightly builds for this pull request without registering. It is updated on every successful build.

[TaranDahl]

Bug behavior:

I gave all of these future tank attackmove missions, but the circled one somehow lost his megamission and moved directly to the mega destination.

[CrimRecya]

I think this should be considered a vanilla bug, and the default behavior can be directly changed. Also needs to be mentioned in the doc.
But what I am not sure about now is: Will only AttackMove.StopWhenTargetAcquired=yes units have such problems?

[TaranDahl]

Will only AttackMove.StopWhenTargetAcquired=yes units have such problems?

Yes, it won't happen if this flag is not set. That is the reason I suspect the locomotor.

[TaranDahl]

Update:
Fix the bug that units in AttackMove cannot correctly exit AttackMove (such as being hit by EMP) when they are forced into other missions.