Fixed a runtime error with the weldfuel reagent.

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@2002 316c924e-a436-60f5-8080-3fe189b3f50e

code/modules/chemical/Chemistry-Reagents.dm

@@ -880,6 +880,8 @@ datum
 			reaction_obj(var/obj/O, var/volume)
 				src = null
 				var/turf/the_turf = get_turf(O)
+				if(!the_turf)
+					return //No sense trying to start a fire if you don't have a turf to set on fire. --NEO
 				var/datum/gas_mixture/napalm = new
 				var/datum/gas/volatile_fuel/fuel = new
 				fuel.moles = 15