Fix for laughing gas leaks in surgery.

Humans breath out same gas mix datum they breathed in.
Works fine because in processing oxygen and CO2 levels in mix are adjusted.
But trace gases remained untouched.
So sedated patient just breathed out N20 at surgeon.

code/modules/mob/living/carbon/human/life.dm

@@ -633,6 +633,7 @@
 				else if(SA_pp > 0.01)	// There is sleeping gas in their lungs, but only a little, so give them a bit of a warning
 					if(prob(20))
 						spawn(0) emote(pick("giggle", "laugh"))
+				SA.moles = 0
 
 		if( (abs(310.15 - breath.temperature) > 50) && !(COLD_RESISTANCE in mutations)) // Hot air hurts :(
 			if(breath.temperature < 260.15)