* Fixes an issue with multiz visholders duplicating (#73835)
## About The Pull Request
I think the inherent issue here has to do with turf refs or something,
but the big problem was I assumed if there was only once source, then
the turf must be new. This was an invalid assumption, since we can add
sources more then once, and | is used
Because of this, each time a shuttle moved, we'd add an extra source for
no reason, and stack extra vis holders. This lead to really bad
clientside lag on some out of repo maps, which is how this issue came to
my attention.
Instead checking if the sources list exists or not solves the problem
pretty handily, so let's do that.
## Why It's Good For The Game
Closes#73834, prevents a potential future OOM
* Fixes an issue with multiz visholders duplicating
---------
Co-authored-by: LemonInTheDark <58055496+LemonInTheDark@users.noreply.github.com>