* Fixes a bug with the immerse element (#77585)
## About The Pull Request
What it says on the tin. This runtime was caught downstream in an away
mission unit test where a mob is placed in a water turf.
Basically the immerse overlay wasn't being added the very first time it
was created, because it wasn't being returned by
`generate_vis_overlay()`. Derp.
It went unnoticed because the overlays are cached and so every
subsequent `add_immerse_overlay()` works fine. And I guess upstream
doesn't have any mobs that spawn in water during tests so it was never
caught.
Also stops `on_init_or_entered()` from needlessly being called twice in
the case of a movable atom in water being initialized before the water
turf. The signal `COMSIG_ATOM_AFTER_SUCCESSFUL_INITIALIZED_ON` already
sees to that.
## Why It's Good For The Game
Fixes a bug
## Changelog
🆑
fix: fixes immerse overlays not being added the first time a mob enters
a water turf
/🆑
* Fixes a bug with the immerse element
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Co-authored-by: Bloop <13398309+vinylspiders@users.noreply.github.com>
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