Another stack of runtime errors dealt with.

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@260 316c924e-a436-60f5-8080-3fe189b3f50e

code/game/objects/items/weapons/mops_cleaners.dm

@@ -71,9 +71,10 @@ MOP
 		for(var/mob/O in viewers(user, null))
 			O.show_message(text("\red <B>[user] begins to clean [A]</B>"), 1)
 		sleep(20)
-		user << "\blue You have finished mopping!"
-		var/turf/U = A.loc
-		src.reagents.reaction(U)
+		if(A)
+			user << "\blue You have finished mopping!"
+			var/turf/U = A.loc
+			src.reagents.reaction(U)
 		if(A) del(A)
 		mopcount++