A couple sanity checks i forgot to include in disposals

These might prove to be pointless but i'd rather be overly cautious about something that crashes a server in 3 seconds flat

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@3191 316c924e-a436-60f5-8080-3fe189b3f50e

code/modules/recycling/disposal.dm

@@ -657,7 +657,8 @@
 				return
 
 			// otherwise, do normal expel from turf
-			expel(H, T, 0)
+			if(H)
+				expel(H, T, 0)
 		..()
 
 	// returns the direction of the next pipe object, given the entrance dir
@@ -795,7 +796,8 @@
 				return
 
 			// otherwise, do normal expel from turf
-			expel(H, T, 0)
+			if(H)
+				expel(H, T, 0)
 
 		spawn(2)	// delete pipe after 2 ticks to ensure expel proc finished
 			del(src)
@@ -1113,13 +1115,15 @@
 		// otherwise, go to the linked object
 		if(linked)
 			var/obj/structure/disposaloutlet/O = linked
-			if(istype(O))
+			if(istype(O) && (H))
 				O.expel(H)	// expel at outlet
 			else
 				var/obj/machinery/disposal/D = linked
-				D.expel(H)	// expel at disposal
+				if(H)
+					D.expel(H)	// expel at disposal
 		else
-			src.expel(H, src.loc, 0)	// expel at turf
+			if(H)
+				src.expel(H, src.loc, 0)	// expel at turf
 		return null
 
 	// nextdir