[MIRROR] [NO GBP] fixes positive viruses being hidden (#2773)

* [NO GBP] fixes positive viruses being hidden (#83576)

## About The Pull Request

#83459 made stealth a function of being equal to or higher than severity
which made a lot of previously visible positive viruses hidden.
Unintended behavior, fixes it.

## Why It's Good For The Game

fix good, most people without HUDs can't see these anyway. It's almost a
QOL thing to just be able to ask a doctor "hey do I have a positive
virus" since if it's perfectly positive, there's nothing really gained
by people not knowing (you, enemies, and friends alike.)

## Changelog

:cl:
fix: positive viruses are no longer hidden.
/:cl:

* [NO GBP] fixes positive viruses being hidden

---------

Co-authored-by: Higgin <[email protected]>
Co-authored-by: NovaBot13 <[email protected]>

code/datums/diseases/advance/advance.dm

@@ -272,7 +272,7 @@
 /datum/disease/advance/proc/assign_properties()
 
 	if(properties?.len)
-		if(properties["stealth"] >= properties["severity"])
+		if(properties["stealth"] >= properties["severity"] && properties["severity"] > 0)
 			visibility_flags |= HIDDEN_SCANNER
 		else
 			visibility_flags &= ~HIDDEN_SCANNER