Rare error when the GC, ML and Megalith make landfall

[Basilisk3]

Describe the bug

This is the same issue as fixed in #5829. It is a rare bug, but it does happen in real games.

The error:

WARNING: *WARNING: No movement effect groups defined for unit ual0401,
Effect groups with bone lists must be defined to play movement effects. 
Add these to the Display.MovementEffects Land. Effects table in unit blueprint. 

The definition of the error is found in Unit.lua, line 3732.

How to reproduce the error:

• Spawn a line of GCs via the Alt+F2 menu (the line must be both on land and in the water)
• Give a movement order to the units you spawned in

Additional context

Related to: #6135; #5924; #5829