fix some blindness issues (#47024)

About The Pull Request

fixes #47020 #47022
I didn't have a max set for the adjust_blindness proc which allowed it to go below zero which meant if you took eye healing chems it would actually make you blind forever, the issue with the wizard spell blinding you permanently was due to a check to see if duration was less than charge_max for genetic spells which was used for making mutate permanent, but also made the blindness spell permament
Why It's Good For The Game

Being blind forever can suck
Changelog

cl
fix: blindness spell now only blinds you temporarily
fix: drinking carrot juice no longer permanently blinds you
/cl

code/modules/mob/status_procs.dm

@@ -32,7 +32,7 @@
   */
 /mob/proc/adjust_blindness(amount)
 	var/old_eye_blind = eye_blind
-	eye_blind += amount
+	eye_blind = max(0, eye_blind + amount)
 	if(!old_eye_blind || !eye_blind && !HAS_TRAIT(src, TRAIT_BLIND))
 		update_blindness()
 /**