Fix old Lua breakage

Works around a problem in the old Lua API where a trait lookup would
not find the correct class and make the script crash.

In this instance, `Game.modData.ObjectCreator.FindType("RallyPoint")`
return `OpenRA.Mods.Common.Effects.RallyPoint` instead of the expected
`OpenRA.Mods.Common.RallyPoint`.

The other change is an oversight from the recent warhead rewrites.

Fixes #6728
Merge pull request #6731 from obrakmann/fix6728_intervention_breakage

Fix old Lua breakage